#include <cstdio>
#include <vector>
#include <algorithm>
#include <stack>
using namespace std;

int N, M;
vector<int> con[100001];
int crt;
int desc[100001], low[100001];
vector<vector<int> > ww;
stack<int> st;

void dfs(int nod) {
    int i;
    st.push(nod);
    for(i = 0; i < con[nod].size(); i++) {
        int u = con[nod][i];
        if(!desc[u]) {
            low[u] = desc[u] = (++crt);
            dfs(u);
            if(low[u] < low[nod])
                low[nod] = low[u];
        } else {
            if(low[nod] > low[u]) {
                low[nod] = low[u];
            }
        }
    }
    if(desc[nod] == low[nod]) {
        ww.push_back(vector<int>());
        while(true) {
            int u = st.top();
            st.pop();
            ww.back().push_back(u);
            if(u == nod)
                break;
        }
    }
}

int main() {
    int i, j;
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);
    scanf("%d %d", &N, &M);
    for(i = 0; i < M; i++) {
        int a, b;
        scanf("%d %d", &a, &b);
        con[a].push_back(b);
    }
    for(i = 1; i <= N; i++) {
        if(!desc[i]) {
            desc[i] = low[i] = (++crt);
            dfs(i);
        }
    }
    printf("%d\n", ww.size());
    for(i = 0; i < ww.size(); i++) {
        for(j = 0; j < ww[i].size(); j++) {
            printf("%d ", ww[i][j]);
        }
        printf("\n");
    }
    return 0;
}