#include<cstdio>
#include<vector>
#define MAX_N 100000
using namespace std;

vector<int>g[MAX_N + 1], scc[MAX_N + 1];
int d[MAX_N + 1], viz[MAX_N + 1], st[MAX_N + 1], n, m, numScc, vf, k;
bool used[MAX_N + 1];

inline int minim(int x, int y) {
    if(x <= y) return x;
    return y;
}

void readGraph() {
    int x, y;
    FILE *fin = fopen("ctc.in","r");
    fscanf(fin,"%d%d",&n,&m);
    for(int i = 0; i < m; i++) {
        fscanf(fin,"%d%d",&x,&y);
        g[x].push_back(y);
    }
    fclose(fin);
}

void DFS(int node) {
    st[++vf] = node;
    used[node] = true;
    d[node] = viz[node] = ++k;

    for(vector<int>::iterator it = g[node].begin(); it != g[node].end(); it++) {
        if(!d[*it]) {
            DFS(*it);
            d[node] = minim(d[node],d[*it]);
        } else if(used[*it]) {
            d[node] = minim(d[node],d[*it]);
        }
    }

    if(d[node] == viz[node]) {
        do {
            scc[numScc].push_back(st[vf]);
            used[st[vf]] = false;
            vf--;
        }while(st[vf + 1] != node);
        numScc++;
    }
}

void DFS_master() {
    for(int i = 1; i <= n; i++)
        if(!viz[i])
            DFS(i);
}

void printSCC() {
    FILE *fout = fopen("ctc.out","w");
    fprintf(fout,"%d\n",numScc);
    for(int i = 0; i < numScc; i++) {
        for(vector<int>::iterator it = scc[i].begin(); it != scc[i].end(); it++)
            fprintf(fout,"%d ",*it);
        fprintf(fout,"\n");
    }
    fclose(fout);
}

int main() {
    readGraph();
    DFS_master();
    printSCC();
    return 0;
}