#include <bits/stdc++.h>

using namespace std;

#ifndef LOCAL
ifstream in("ctc.in");
ofstream out("ctc.out");
#define cin in
#define cout out
#endif // LOCAL

const int NMAX = 1e5 + 7;
vector<int> g[NMAX];
vector<int> rg[NMAX];
vector<vector<int>> cc;
vector<int> pre, cntc;

int viz[NMAX];

void dfs(int node) {
    if(viz[node] == 1) return;
    viz[node] = 1;

    for(auto vec : g[node]) dfs(vec);

    pre.push_back(node);
}

void col(int node) {
    if(viz[node] == 2) return;
    viz[node] = 2; cntc.push_back(node);

    for(auto vec : rg[node]) col(vec);
}

int main()
{
    int n, m; cin >> n >> m;
    for(int i = 0; i < m; i++) {
        int x, y; cin >> x >> y;
        g[x].push_back(y);
        rg[y].push_back(x);
    }

    for(int i = 1; i <= n; i++) {
        if(viz[i] == 0) dfs(i);
    }
    reverse(pre.begin(), pre.end());

    for(auto i : pre) {
        if(viz[i] == 1) {
            cntc.clear();
            col(i);
            cc.push_back(cntc);
        }
    }

    cout << cc.size() << '\n';
    for(auto c : cc) {
        for(auto e : c) cout << e << " ";
        cout << '\n';
    }

    return 0;
}