
import collection.mutable.ArrayBuffer
import scala.reflect.ClassTag
import scala.language.implicitConversions

trait Graph { 
    case class Edge[T:Numeric](from : Int, to : Int, cost : T)

    class Edges[T:Numeric](val data : ArrayBuffer[Edge[T]]) {
        def size = data.size
    }
    object Edges {
        def apply[T:Numeric](xs : Edge[T]*) = new Edges(ArrayBuffer(xs:_*))
        implicit def toUnderLying[T](x:Edges[T]) = x.data
    }

    class WeightedGraph[T:Numeric](val size : Int, val data : Array[Edges[T]]) {
        def this(size : Int) = this(size, Array.fill(size)(Edges()))
    }
    object WeightedGraph {
        // def apply[T:Numeric](size : Int) = new WeightedGraph[T](size)
        implicit def toUnderLying[T](x:WeightedGraph[T]) = x.data
    }

    class UnWeightedGraph[T:Numeric](val size : Int, val data: Array[ArrayBuffer[T]]) {
        def this(size : Int) = this(size, Array.fill(size)(ArrayBuffer[T]()))
    }
    object UnWeightedGraph {
        // def apply[T:Numeric](size : Int) = new UnWeightedGraph[T](size)
        implicit def toUnderLying[T](x:UnWeightedGraph[T]) = x.data
    }
   
    class Matrix[T:Numeric:ClassTag](val row : Int, val col : Int, val data : Array[Array[T]]) {
        def this(row : Int, col : Int) = this(row, col, Array.fill(row, col)(implicitly[Numeric[T]].zero))
        def this(size : Int) = this(size, size)
    }
    object Matrix {
        implicit def toUnderLying[T](x:Matrix[T]) = x.data
    }
}

object BellmanFord extends Graph {
    import Edges._

    // return ArrayBuffer() when find a negative cycle
    def bellmanFord[T:ClassTag](edges : Edges[T], V : Int, s : Int, INF : T)(implicit num : Numeric[T]) : Array[T] = {
        val dist = Array.fill[T](V)(INF)
        dist(s) = num.zero
        for (i <- 1 to V) {
            for (e <- edges) {
                if(dist(e.from) != INF 
                    && num.lt(num.plus(dist(e.from), e.cost), dist(e.to))) {
                        dist(e.to) = num.plus(dist(e.from), e.cost)
                        if (i == V-1 && e.to == V-1) return Array.empty
                    }
            }
        }
        dist
    }
}

import BellmanFord._

object Main {
    def main(args: Array[String]) = {
        val sc = new java.util.Scanner(System.in)
        val N, M = sc.nextInt
        val edges = Edges[Long]()
        for (_ <- 1 to M) {
            val s, t = sc.nextInt
            val c : Long = sc.nextLong
            edges += Edge[Long](s-1, t-1, -c)
        }
        // println(edges.toList)
        val res = bellmanFord(edges, N, 0, Long.MaxValue)
        // println(res.toList)
        if (res.isEmpty) println("inf")
        else {
            println(-res(N-1))
        }
    }
}