import java.io._
import java.util.StringTokenizer
import scala.util.control.Breaks.{breakable,break}

object Main extends App {
  val in = new InputReader(System.in)
  val pw = new PrintWriter(System.out)

  // val a = new Array[Int](N)

  val N, K = in.next().toInt

  if (N == 2) {
    if (K == 0) {
      println(1)
      println(1, 2)
    }
    else {
      println(-1)
    }
  }
  else if (N == 3) {
    if (K == 0) {
      println(3)
      println(1, 2)
      println(2, 3)
      println(3, 1)
    }
    else if (K == 1) {
      println(2)
      println(1, 2)
      println(2, 3)
    }
    else
      println(-1)
  }
  else {
    if (K == N) {
      pw.println(N)
      pw.println(N, 1)
      for (i <- 1 until N)
        pw.println(i, i+1)
    }
    else {
      var tmp = ((N-2) * (N-1)) / 2

      if (tmp < K)
        pw.println(-1)
      else {
        var ans: List[(Int, Int)] = Nil

        for (i <- 2 to N) {
          ans = (i, 1) :: ans
        }


        var l = 2
        var r = 3
        while(tmp > K) {
          ans = (l, r) :: ans

          if (r == N) {
            l += 1
            r = l + 1
          }
          else {
            r += 1
          }

          tmp -= 1
        }

        pw.println(ans.length)
        ans.foreach {case (a, b) => pw.println(s"$a $b")}
      }
    }

    pw.flush()
  }
}


class InputReader(stream: InputStream) {
  private val reader = new BufferedReader(new InputStreamReader(stream))
  private var tokenizer: StringTokenizer = new StringTokenizer(reader.readLine())
  def next(): String = {
    while (!tokenizer.hasMoreTokens()) {
      tokenizer = new StringTokenizer(reader.readLine())
    }
    tokenizer.nextToken()
  }
}
