import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.math.BigDecimal; import java.math.RoundingMode; import java.util.*; import java.io.File; import java.io.FileDescriptor; import java.io.FileOutputStream; import java.io.OutputStream; import java.io.UncheckedIOException; import java.lang.reflect.Field; import java.nio.CharBuffer; import java.nio.charset.CharacterCodingException; import java.nio.charset.CharsetEncoder; import java.nio.charset.StandardCharsets; public class Main { static final long MOD=1000000007; static final long MOD1=998244353; static int ans=0; public static void main(String[] args){ PrintWriter out = new PrintWriter(System.out); InputReader sc=new InputReader(System.in); int N = sc.nextInt(); int M = sc.nextInt(); int ans = 0; ArrayList[] E = new ArrayList[N]; for (int i = 0; i < E.length; i++) { E[i] = new ArrayList<>(); } UnionFindTree uTree = new UnionFindTree(N); int[] deg = new int[N]; for (int i = 0; i < M; i++) { int a = sc.nextInt()-1; int b = sc.nextInt()-1; deg[b]++; uTree.union(a, b, 1); E[a].add(b); } ArrayList[] group = new ArrayList[N]; for (int i = 0; i < group.length; i++) { group[i] = new ArrayList<>(); } for (int i = 0; i < N; i++) { group[uTree.find(i)].add(i); } ArrayList anStrings = new ArrayList<>(); for (int i = 0; i < group.length; i++) { if(group[i].size()<=1)continue; ArrayDeque deq = new ArrayDeque<>(); ArrayList topo = new ArrayList<>(); for (int v: group[i]) { if(deg[v]==0)deq.add(v); } int c = 0; while (!deq.isEmpty()) { int v = deq.pollFirst(); topo.add(v); c++; for (Integer to: E[v]) { deg[to]--; if (deg[to]==0) { deq.add(to); } } } for (int j = 0; j < topo.size()-1; j++) { anStrings.add((topo.get(j)+1)+" "+(topo.get(j+1)+1)); } if (c==group[i].size()) { ans += group[i].size()-1; }else { ans += group[i].size(); anStrings.add((topo.get(topo.size()-1)+1)+" "+(topo.get(0)+1)); } } out.println(ans); for (String string : anStrings) { out.println(string); } out.flush(); } static class UnionFindTree{ int[] par; int[] rank; int[] size; int[] diff_weight; int arraysize; public UnionFindTree(int n) { this.par=new int[n]; this.rank=new int[n]; this.size=new int[n]; this.diff_weight=new int[n]; arraysize=n; for (int i = 0; i < arraysize; i++) { set(i); } } public void set(int i) { par[i]=i; rank[i]=0; size[i]=1; diff_weight[i]=0; } public void union(int x,int y,int w) { w += weight(x); w -= weight(y); int rootx=find(x); int rooty=find(y); if (rootx==rooty) { return; } if (rank[rootx]>rank[rooty]) { par[rooty]=rootx; diff_weight[rooty] = w; size[rootx]+=size[rooty]; } else if (rank[rootx]= lenbuf) { curbuf = 0; try { lenbuf = in.read(buffer); } catch (IOException e) { throw new InputMismatchException(); } if (lenbuf <= 0) return false; } return true; } private int readByte() { if (hasNextByte()) return buffer[curbuf++]; else return -1; } private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); } private void skip() { while (hasNextByte() && isSpaceChar(buffer[curbuf])) curbuf++; } public boolean hasNext() { skip(); return hasNextByte(); } public String next() { if (!hasNext()) throw new NoSuchElementException(); StringBuilder sb = new StringBuilder(); int b = readByte(); while (!isSpaceChar(b)) { sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } public int nextInt() { if (!hasNext()) throw new NoSuchElementException(); int c = readByte(); while (isSpaceChar(c)) c = readByte(); boolean minus = false; if (c == '-') { minus = true; c = readByte(); } int res = 0; do { if (c < '0' || c > '9') throw new InputMismatchException(); res = res * 10 + c - '0'; c = readByte(); } while (!isSpaceChar(c)); return (minus) ? -res : res; } public long nextLong() { if (!hasNext()) throw new NoSuchElementException(); int c = readByte(); while (isSpaceChar(c)) c = readByte(); boolean minus = false; if (c == '-') { minus = true; c = readByte(); } long res = 0; do { if (c < '0' || c > '9') throw new InputMismatchException(); res = res * 10 + c - '0'; c = readByte(); } while (!isSpaceChar(c)); return (minus) ? -res : res; } public double nextDouble() { return Double.parseDouble(next()); } public int[] nextIntArray(int n) { int[] a = new int[n]; for (int i = 0; i < n; i++) a[i] = nextInt(); return a; } public double[] nextDoubleArray(int n) { double[] a = new double[n]; for (int i = 0; i < n; i++) a[i] = nextDouble(); return a; } public long[] nextLongArray(int n) { long[] a = new long[n]; for (int i = 0; i < n; i++) a[i] = nextLong(); return a; } public char[][] nextCharMap(int n, int m) { char[][] map = new char[n][m]; for (int i = 0; i < n; i++) map[i] = next().toCharArray(); return map; } } }