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

vector<int>g[MAX_N + 1], scc[MAX_N + 1];
int visitedTime[MAX_N + 1], lowTime[MAX_N + 1], st[MAX_N + 1], n, m, time, vf, numSCC;
bool onStack[MAX_N + 1];

inline int minim(int a, int b) {
    if(a <= b) return a;
    return b;
}

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

void DFS(int node) {
    vector<int>::iterator it;
    st[++vf] = node;
    onStack[node] = true;
    visitedTime[node] = lowTime[node] = ++time;
    for(it = g[node].begin(); it != g[node].end(); it++) {
        if(!visitedTime[*it]) {
            DFS(*it);
            lowTime[node] = minim(lowTime[node],lowTime[*it]);
        } else if(onStack[*it])
            lowTime[node] = minim(lowTime[node],lowTime[*it]);
    }
    if(visitedTime[node] == lowTime[node]) {
        do {
            scc[numSCC].push_back(st[vf]);
            onStack[st[vf]] = false;
            vf--;
        }while(st[vf + 1] != node);
        numSCC++;
    }
}

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

void printSCC() {
    int i, j, k;
    FILE *fout = fopen("ctc.out","w");
    fprintf(fout,"%d\n",numSCC);
    for(i = 0; i < numSCC; i++) {
        k = scc[i].size();
        for(j = 0; j < k; j++)
            fprintf(fout,"%d ",scc[i][j]);
        fprintf(fout,"\n");
    }
    fclose(fout);
}

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