import java.io.BufferedReader
import java.io.InputStream
import java.io.InputStreamReader
import java.lang.AssertionError
import java.util.*
import kotlin.math.abs
import kotlin.math.max
import kotlin.math.min

val MOD = 998244353

class UnionFind(n: Int) {
  private val par = IntArray(n){it}
  private val rank = IntArray(n){1} // 集合の要素数
  private val visits = IntArray(n) // 訪れた場所をfind毎に用意するのがもったいないのでつかいまわす

  fun find(x: Int): Int {
    var ptr = 0
    var i = x
    while(par[i] != i) {
      visits[ptr++] = i
      i = par[i]
    }

    for (j in 0 until ptr) {
      par[visits[j]] = i
    }
    return i
  }

  private fun merge(node: Int, rt: Int): Int {
    par[node] = rt
    rank[rt] += rank[node]
    return rt
  }

  fun unite(x: Int, y: Int): Boolean {
    val x1 = find(x)
    val y1 = find(y)
    return if (x1 == y1) false
    else {
      if (rank[x1] < rank[y1])
        merge(x1, y1)
      else
        merge(y1, x1)

      true
    }
  }

  fun isSame(x: Int, y: Int) = find(x) == find(y)

  fun isRoot(x: Int) = par[x] == x

  /**
   * xを解決する必要がないときは直にrankをみる
   */
  fun cntNodes(x: Int): Int = rank[find(x)]

  fun inspect() = run{par}
}

/**
 * listをgroupに分けたいときに、Array(N){mutableList<Int>()}が重いので、軽い実装
 *
 * @param N 要素のサイズ
 * @param M グループのサイズ
 */
class GroupedArray(val N: Int, val M: Int) {
  private val rt = IntArray(M){-1}
  private val next = IntArray(N){-2}
  private val cnt = IntArray(M)

  fun setGroup(i: Int, g: Int) {
    next[i] = rt[g]
    rt[g] = i
    cnt[g]++
  }

  fun elements(g: Int): IntArray? {
    if (cnt[g] == 0) return null

    val res = IntArray(cnt[g])
    var cur = rt[g]
    for (i in 0 until cnt[g]) {
      res[i] = cur
      cur = next[cur]
    }

    return res
  }
}

/**
 * 連結成分毎にsubgraphに分けて、subgraph上で番号を振り直す処理をまとめたもの
 */
class GroupedByDSU(private val N: Int,
                   private val M: Int,
                   private val from: IntArray,
                   private val to: IntArray)
{
  data class Group(val N: Int, val from: IntArray, val to: IntArray)

  private val mapping = IntArray(N) // zip_id -> node_id
  private val inv = IntArray(N) // node_id -> zip_id

  private val grp = IntArray(N)
  private val grpNodes = GroupedArray(N, N)
  private val grpEdges = GroupedArray(M, N)

  fun build() {
    val uf = UnionFind(N)
    for (i in 0 until M) {
      uf.unite(from[i], to[i])
    }
    for (i in 0 until N) {
      grp[i] = uf.find(i)
      grpNodes.setGroup(i, grp[i])
    }
    for (i in 0 until M) {
      val g = grp[from[i]]
      grpEdges.setGroup(i, g)
    }
  }

  /**
   * @return (grp, zip_id -> node_id のmapping)
   */
  fun get(g: Int): Pair<Group, IntArray>? {
    val nodes = grpNodes.elements(g) ?: return null
    val edges = grpEdges.elements(g) ?: return null
    for (i in nodes.indices) {
      val v = nodes[i]
      mapping[i] = v
      inv[v] = i
    }

    val gFrom = IntArray(edges.size)
    val gTo = IntArray(edges.size)
    for (i in edges.indices) {
      gFrom[i] = inv[from[edges[i]]]
      gTo[i] = inv[to[edges[i]]]
    }
    val group = Group(nodes.size, gFrom, gTo)
    return Pair(group, mapping)
  }
}

fun packDGraph(n: Int, from: IntArray, to: IntArray): Array<IntArray> {
  val p = IntArray(n)
  val m = from.size
  for (i in 0 until m) {
    ++p[from[i]]
  }
  val g = Array(n){IntArray(p[it])}
  for (i in 0 until m) {
    g[from[i]][--p[from[i]]] = to[i]
  }
  return g
}
/**
 * @return node->order　じゃなくて、nodeのリストを返す。
 */
fun topologicalSort(n: Int, g: Array<IntArray>): IntArray? {
  val res = IntArray(n){-1}
  var ptr = 0
  val que = ArrayDeque<Int>()
  val deg = IntArray(n)

  for (v in 0 until n) {
    for (o in g[v]) {
      deg[o]++
    }
  }

  for (v in 0 until n) {
    if (deg[v] == 0) que.add(v)
  }

  while(que.isNotEmpty()) {
    val v = que.poll()
    res[ptr++] = v
    for (i in g[v].indices) {
      val o = g[v][i]
      if (--deg[o] == 0) que.add(o)
    }
  }

  // 全部に順序がつかないとループがあったってこと
  // グラフにでてこないノードにも順序がつく
  return if (ptr < n) null else res
}

class Solver(stream: InputStream, private val out: java.io.PrintWriter) {
  private val reader = BufferedReader(InputStreamReader(stream), 32768)

  fun solve() {
    val (N, M) = na(2)
    val (from, to) = na2(M, -1)

    val ans = mutableListOf<Pair<Int, Int>>()
    val grouped = GroupedByDSU(N, M, from, to)
    grouped.build()
    for (gId in 0 until N) {
      val (grp, map) = grouped.get(gId) ?: continue
      val n = grp.N
      val g = packDGraph(n, grp.from, grp.to)
      val top = topologicalSort(n, g)
      if (top == null) {
        // 一回転
        for (i in 0 until n) {
          ans += Pair(map[i], map[(i + 1)%n])
        }
      }
      else {
        // 一直線
        for (o in 0 until n - 1) {
          ans += Pair(map[top[o]], map[top[o + 1]])
        }
      }
    }

    out.println(ans.size)
    for (i in ans) {
      out.println("${i.first+1} ${i.second+1}")
    }
  }













































  private val isDebug = try {
    // なんか本番でエラーでる
    System.getenv("MY_DEBUG") != null
  } catch (t: Throwable) {
    false
  }

  private var tokenizer: StringTokenizer? = null
  private fun next(): String {
    while (tokenizer == null || !tokenizer!!.hasMoreTokens()) {
      tokenizer = StringTokenizer(reader.readLine())
    }
    return tokenizer!!.nextToken()
  }

  private fun ni() = next().toInt()
  private fun nl() = next().toLong()
  private fun ns() = next()
  private fun na(n: Int, offset: Int = 0): IntArray {
    return IntArray(n) { ni() + offset }
  }
  private fun nal(n: Int, offset: Int = 0): LongArray {
    val res = LongArray(n)
    for (i in 0 until n) {
      res[i] = nl() + offset
    }
    return res
  }

  private fun na2(n: Int, offset: Int = 0): Array<IntArray> {
    val a  = Array(2){IntArray(n)}
    for (i in 0 until n) {
      for (e in a) {
        e[i] = ni() + offset
      }
    }
    return a
  }

  private inline fun debug(msg: () -> String) {
    if (isDebug) System.err.println(msg())
  }

  /**
   * コーナーケースでエラー出たりするので、debug(dp[1])のように添え字付きの場合はdebug{}をつかうこと
   */
  private inline fun debug(a: LongArray) {
    debug { a.joinToString(" ") }
  }

  private inline fun debug(a: IntArray) {
    debug { a.joinToString(" ") }
  }

  private inline fun debug(a: BooleanArray) {
    debug { toString(a) }
  }

  private inline fun toString(a: BooleanArray) = run{a.map { if (it) 1 else 0 }.joinToString("")}

  private inline fun debugDim(A: Array<LongArray>) {
    if (isDebug) {
      for (a in A) {
        debug(a)
      }
    }
  }
  private inline fun debugDim(A: Array<IntArray>) {
    if (isDebug) {
      for (a in A) {
        debug(a)
      }
    }
  }
  private inline fun debugDim(A: Array<BooleanArray>) {
    if (isDebug) {
      for (a in A) {
        debug(a)
      }
    }
  }

  /**
   * 勝手にimport消されるのを防ぎたい
   */
  private fun hoge() {
    min(1, 2)
    max(1, 2)
    abs(-10)
  }

  private inline fun assert(b: Boolean) = run{if (!b) throw AssertionError()}
  private inline fun assert(b: Boolean, f: () -> String) = run{if (!b) throw AssertionError(f())}
}

fun main() {
  val out = java.io.PrintWriter(System.out)
  Solver(System.`in`, out).solve()
  out.flush()
}