#include <iostream>
#include <fstream>
#include <vector>
#include <stack>

using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");

#define pb push_back
typedef long long ll;
const int NMax = 1e5 + 5;
const int inf = 1e9;

int N,M,nrComp,nrInStack;
int lowPoint[NMax],idx[NMax];
vector<int> v[NMax];
vector<int> comp[NMax];
stack<int> st;

void dfs(int);

int main() {
    in>>N>>M;
    for (int i=1;i<=M;++i) {
        int x,y;
        in>>x>>y;
        v[x].pb(y);
    }

    for (int i=1;i<=N;++i) {
        if (idx[i] != 0) {
            continue;
        }

        dfs(i);
    }

    out<<nrComp<<'\n';
    for (int i=1;i<=nrComp;++i) {
        for (int k=0;k < (int)comp[i].size();++k) {
            out<<comp[i][k]<<' ';
        }
        out<<'\n';
    }

    in.close();out.close();
    return 0;
}

void dfs(int nod) {
    idx[nod] = lowPoint[nod] = ++nrInStack;
    st.push(nod);

    for (int k=0;k < (int)v[nod].size();++k) {
        int next = v[nod][k];

        if (idx[next] == 0) {
            dfs(next);
        }
        lowPoint[nod] = min(lowPoint[nod],lowPoint[next]);
    }

    if (lowPoint[nod] == idx[nod]) {
        int top;
        ++nrComp;
        do {
            top = st.top();
            st.pop();
            idx[top] = lowPoint[top] = inf;
            comp[nrComp].pb(top);
        }
        while (top != nod);
    }
}