import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


int root(int[] uf, int u) {
  return (uf[u] < 0) ? u : (uf[u] = uf.root(uf[u]));
}
bool connect(int[] uf, int u, int v) {
  u = uf.root(u);
  v = uf.root(v);
  if (u == v) return false;
  if (uf[u] > uf[v]) swap(u, v);
  uf[u] += uf[v];
  uf[v] = u;
  return true;
}


int N, M;
int[] A, B;

int[][] G;

int[] vis;
int[] us;

bool dfs(int u) {
  bool ret = true;
  vis[u] = 1;
  foreach (i; G[u]) {
    const v = A[i] ^ B[i] ^ u;
    final switch (vis[v]) {
      case 0: {
        if (!dfs(v)) {
          ret = false;
        }
      } break;
      case 1: {
        ret = false;
      } break;
      case 2: {
        //
      } break;
    }
  }
  vis[u] = 2;
  us ~= u;
  return ret;
}

void main() {
  try {
    for (; ; ) {
      N = readInt();
      M = readInt();
      A = new int[M];
      B = new int[M];
      foreach (i; 0 .. M) {
        A[i] = readInt() - 1;
        B[i] = readInt() - 1;
      }
      
      G = new int[][N];
      foreach (i; 0 .. M) {
        G[A[i]] ~= i;
      }
      
      auto uf = new int[N];
      uf[] = -1;
      foreach (i; 0 .. M) {
        uf.connect(A[i], B[i]);
      }
      auto uss = new int[][N];
      foreach (u; 0 .. N) {
        uss[uf.root(u)] ~= u;
      }
      
      alias Edge = Tuple!(int, "a", int, "b");
      Edge[] ans;
      vis = new int[N];
      foreach (r; 0 .. N) {
        if (uss[r]) {
          bool dag = true;
          us = [];
          foreach (u; uss[r]) {
            if (vis[u] == 0) {
              if (!dfs(u)) {
                dag = false;
              }
            }
          }
          us.reverse;
          debug {
            writeln(us, " ", dag);
          }
          const usLen = cast(int)(us.length);
          foreach (j; 0 .. usLen - 1) {
            ans ~= Edge(us[j], us[j + 1]);
          }
          if (!dag) {
            ans ~= Edge(us[usLen - 1], us[0]);
          }
        }
      }
      
      writeln(ans.length);
      foreach (e; ans) {
        writeln(e.a + 1, " ", e.b + 1);
      }
    }
  } catch (EOFException e) {
  }
}