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

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

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

int N,M,nrComp;
bool inComp[NMax],pls[NMax],mns[NMax];
vector<int> v[NMax],conv[NMax],comp[NMax];
stack<int> st;

void dfs1(int);
void dfs2(int);

int main() {
    in>>N>>M;
    while (M--) {
        int x,y;
        in>>x>>y;

        v[x].pb(y);
        conv[y].pb(x);
    }

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

        dfs1(i);
        dfs2(i);

        ++nrComp;
        while (st.size()) {
            int node = st.top();
            st.pop();

            if (pls[node] && mns[node]) {
                comp[nrComp].pb(node);
                inComp[node] = true;
            }

            pls[node] = false;
            mns[node] = false;
        }
    }

    out<<nrComp<<'\n';
    for (int k=1;k <= nrComp;++k) {
        for (int node : comp[k]) {
            out<<node<<' ';
        }
        out<<'\n';
    }

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

void dfs1(int node) {
    pls[node] = true;
    st.push(node);

    for (int nxt : v[node]) {
        if (pls[nxt] || inComp[nxt]) {
            continue;
        }

        dfs1(nxt);
    }
}

void dfs2(int node) {
    mns[node] = true;
    if (!pls[node]) {
        st.push(node);
    }

    for (int nxt : conv[node]) {
        if (mns[nxt] || inComp[nxt]) {
            continue;
        }

        dfs2(nxt);
    }
}