#include <cstdio>
#include <bitset>
#include <vector>

#define NMAX 100001
#define INF (1 << 30)

using namespace std;

bitset<NMAX> onStack;
vector<int> children[NMAX];
vector<vector<int> > solution;
vector<int> st;
int n, m, count, index[NMAX], minim[NMAX];

void readInput() {
  freopen("ctc.in", "r", stdin);
  freopen("ctc.out", "w", stdout);
  int a, b;
  scanf("%d %d", &n, &m);
  for (int i = 0; i < m; i++) {
    scanf("%d %d", &a, &b);
    children[a].push_back(b);
  }
  for (int i = 1; i <= n; i++) {
    index[i] = INF;
  }
}

void push(int idx) {
  onStack[idx] = 1;
  index[idx] = minim[idx] = ++count;
  st.push_back(idx);
//  printf("Push %d with %d\n", idx, minim[idx]);
}

void pop(int idx) {
  if (minim[idx] == index[idx]) {
    int top;
    solution.push_back(vector<int>());
    do {
      top = st.back();
      onStack[top] = 0;
      st.pop_back();
      solution.back().push_back(top);
//      printf("Pop %d with %d\n", top, minim[top]);
    } while (top != idx);
  }
}

void visit(int idx) {
  push(idx);
  for (size_t i = 0; i < children[idx].size(); i++) {
    int child = children[idx][i];
    if (index[child] == INF) {
      visit(child);
      minim[idx] = min(minim[idx], minim[child]);
    } else if (onStack[child]) {
      minim[idx] = min(minim[idx], index[child]);
    }
  }
  pop(idx);
}

int main() {
  readInput();
  for (int i = 1; i <= n; i++) {
    if (index[i] == INF) {
      visit(i);
    }
  }
  printf("%u\n", solution.size());
  for (size_t i = 0; i < solution.size(); i++) {
    for (size_t j = 0; j < solution[i].size(); j++) {
      printf("%d ", solution[i][j]);
    }
    printf("\n");
  }
  return 0;
}