object Main {
  import java.io.{BufferedReader, InputStream, InputStreamReader}
  import java.util.StringTokenizer
  import scala.reflect.ClassTag

  def main(args: Array[String]): Unit = {
    val out = new java.io.PrintWriter(System.out)
    new Main(out, new InputReader(System.in)).solve()
    out.flush()
  }

  private val oj = System.getenv("ATCODER_DEBUG") == null
  def DEBUG(f: => Unit): Unit = {
    if (!oj){ f }
  }
  def debug(as: Array[Boolean]): Unit = if (!oj){ debug(as.map(x => if(x) "1" else "0").mkString) }
  def debug(as: Array[Int]): Unit = if (!oj){ debug(as.mkString(" ")) }
  def debug(as: Array[Long]): Unit =if (!oj){ debug(as.mkString(" ")) }
  def debugDim(m: Array[Array[Long]]): Unit = if (!oj){
    REP(m.length) { i =>
      debug(m(i))
    }
  }
  def debugDimFlip(m: Array[Array[Long]]): Unit = if (!oj){
    REP(m(0).length) { j =>
      REP(m.length) { i =>
        System.err.print(m(i)(j))
        System.err.print(" ")
      }
      System.err.println()
    }
  }
  def debug(s: => String): Unit = DEBUG {
    System.err.println(s)
  }
  def debugL(num: => Long): Unit = DEBUG {
    System.err.println(num)
  }

  class InputReader(val stream: InputStream) {
    private val reader = new BufferedReader(new InputStreamReader(stream), 32768)
    private var tokenizer: StringTokenizer = _

    def next(): String = {
      while (tokenizer == null || !tokenizer.hasMoreTokens)
        tokenizer = new StringTokenizer(reader.readLine)
      tokenizer.nextToken
    }

    def nextInt(): Int = Integer.parseInt(next())
    def nextLong(): Long = java.lang.Long.parseLong(next())
    def nextChar(): Char = next().charAt(0)

    def ni(): Int = nextInt()
    def nl(): Long = nextLong()
    def nc(): Char = nextChar()
    def ns(): String = next()
    def ns(n: Int): Array[Char] = ns().toCharArray
    def na(n: Int, offset: Int = 0): Array[Int] = map(n)(_ => ni() + offset)
    def na2(n: Int, offset: Int = 0): (Array[Int], Array[Int]) = {
      val A1, A2 = Array.ofDim[Int](n)
      REP(n) { i =>
        A1(i) = ni() + offset
        A2(i) = ni() + offset
      }
      (A1, A2)
    }
    def nm(n: Int, m: Int): Array[Array[Int]] = {
      val A = Array.ofDim[Int](n, m)
      REP(n) { i =>
        REP(m) { j =>
          A(i)(j) = ni()
        }
      }
      A
    }
    def nal(n: Int): Array[Long] = map(n)(_ => nl())
    def nm_c(n: Int, m: Int): Array[Array[Char]] = map(n) (_ => ns(m))
  }

  def REP(n: Int, offset: Int = 0)(f: Int => Unit): Unit = {
    var i = offset
    val N = n + offset
    while(i < N) { f(i); i += 1 }
  }
  def REP_r(n: Int, offset: Int = 0)(f: Int => Unit): Unit = {
    var i = n - 1 + offset
    while(i >= offset) { f(i); i -= 1 }
  }
  def TO(from: Int, to: Int)(f: Int => Unit): Unit = {
    REP(to - from + 1, from) { i =>
      f(i)
    }
  }
  def map[@specialized A: ClassTag](n: Int, offset: Int = 0)(f: Int => A): Array[A] = {
    val res = Array.ofDim[A](n)
    REP(n)(i => res(i) = f(i + offset))
    res
  }

  def sumL(as: Array[Int]): Long = {
    var s = 0L
    REP(as.length)(i => s += as(i))
    s
  }
  def cumSum(as: Array[Int]): Array[Long] = {
    val cum = Array.ofDim[Long](as.length + 1)
    REP(as.length) { i =>
      cum(i + 1) = cum(i) + as(i)
    }
    cum
  }
}

class Main(out: java.io.PrintWriter, sc: Main.InputReader) {
  import sc._
  import Main._
  import java.util.Arrays.sort

  import scala.collection.mutable
  import math.{abs, max, min}
  import mutable.ArrayBuffer

  // toIntとか+7とかするならvalにしろ
  @inline private def MOD = 1000000007

  case class Entry(v: Int, c: Int)
  type G = Array[ArrayBuffer[Entry]]

  def solve(): Unit = {
    val N, M, P = ni()
    val g1, revG = Array.fill[ArrayBuffer[Entry]](N)(ArrayBuffer())
    REP(M) { _ =>
      val a, b = ni() - 1
      val c = ni()
      revG(b) += Entry(a, c)
      g1(a) += Entry(b, c)
    }

    val (_, _, q1, _) = traceBfs(g1, 0)
    val (_, _, qRev, _) = traceBfs(revG, N - 1)
    val r1, rn = Array.ofDim[Boolean](N)
    r1(0) = true
    rn(N - 1) = true
    REP(N) { i =>
      val v = q1(i)
      r1(v) = true
    }
    REP(N) { i =>
      val v = qRev(i)
      rn(v) = true
    }

    val reahable = Array.ofDim[Boolean](N)
    REP(N) { i =>
      reahable(i) = r1(i) && rn(i)
    }

    debug(reahable)

    val g = Array.fill[ArrayBuffer[Entry]](N)(ArrayBuffer())
    REP(N) { v =>
      if (reahable(v)) {
        REP(revG(v).length) { i =>
          val e = revG(v)(i)
          g(e.v) += Entry(v, e.c)
        }
      }
    }

    if (topologicalSort(g) == null) {
      out.println(-1)
      return
    }

    val INF = -1e18.toLong
    val dp = Array.fill[Long](N)(INF)
    dp(0) = 0
    REP(N) { _ =>
      REP(N) { v =>
        REP(g(v).length) { j =>
          if (dp(v) != INF) {
            val u = g(v)(j)
            if (dp(u.v) < dp(v) + u.c - P) {
              dp(u.v) = dp(v) + u.c - P
            }
          }
        }
      }
    }
    out.println(max(0, dp(N - 1)))
  }

  /**
    * @return 閉路の場合はnull
    */
  def topologicalSort(g: G): Array[Int] = {
    val n = g.length
    val L = Array.ofDim[Int](n)
    var ptr = 0
    val S = Array.ofDim[Int](n)
    var last, cur = 0
    val deg = Array.ofDim[Int](n)
    REP(n) { i =>
      REP(g(i).length) { j =>
        deg(g(i)(j).v) += 1
      }
    }

    REP(n) { i =>
      if (deg(i) == 0) {
        S(last) = i
        last += 1
      }
    }

    while(cur < last) {
      val v = S(cur)
      cur += 1
      L(ptr) = v
      ptr += 1

      REP(g(v).length) { i =>
        val u = g(v)(i).v
        deg(u) -= 1
        if (deg(u) == 0) {
          S(last) = u
          last += 1
        }
      }
    }

    // 閉路チェック
    REP(n) { i =>
      if (deg(i) > 0) return null
    }
    L
  }

  /**
    * @return (depth, parent, queue, length)
    */
  def traceBfs(g: G, rt: Int = 0): (Array[Int], Array[Int], Array[Int], Int) = {
    val n = g.length
    val INF = 1e9.toInt + 10
    val q, p = Array.ofDim[Int](n)
    q(0) = rt
    p(rt) = -1
    val d = Array.fill[Int](n)(INF)
    d(rt) = 0
    var cur = 0
    var last = 1
    while (cur < last) {
      val v = q(cur)
      REP(g(v).length) { i =>
        val u = g(v)(i).v
        if (d(u) == INF) {
          d(u) = d(v) + 1
          p(u) = v
          q(last) = u
          last += 1
        }
      }
      cur += 1
    }
    (d, p, q, cur)
  }
}