#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<int> postorder;
int viz[NMAX];
int color[NMAX];

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

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

    postorder.push_back(node);
}

void col(int node, int c) {
    color[node] = c;
    for(auto vec : rg[node]) {
        if(color[vec] == -1) col(vec, c);
    }
}

vector<vector<int>> ans;

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++) dfs(i);
    reverse(postorder.begin(), postorder.end());

    int c = 0;
    for(auto e : postorder) {
        if(color[e] == -1) col(e, c++);
    }

    ans.resize(c);
    for(int i = 1; i <= n; i++) ans[color[i]].push_back(i);

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

    return 0;
}