#include <bits/stdc++.h>

using namespace std;
#ifndef HOME
ifstream fin("ctc.in");
ofstream fout("ctc.out");
#else
ifstream fin("ciorna.in");
ofstream fout("ciorna.out");
#endif
const int N = 1e5;
bool vis[N + 5];
vector <int> g[N + 5], g_t[N + 5];
vector <int> topsort;
vector <vector <int>> ctc;
void dfs(int u) {
    vis[u] = true;
    for(int v : g[u]) if(!vis[v])
        dfs(v);
    topsort.push_back(u);
}
void dfs_t(int u) {
    vis[u] = true;
    for(int v : g_t[u]) if(!vis[v])
        dfs_t(v);
    ctc.back().push_back(u);
}

int main()
{
    int n, m, u, v;
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
        fin >> u >> v,
        g[u].push_back(v),
        g_t[v].push_back(u);
    for(int i = 1; i <= n; i++) if(!vis[i])
        dfs(i);
    memset(vis, 0, sizeof(vis));
    reverse(topsort.begin(), topsort.end());
    for(int u : topsort) if(!vis[u]) {
        ctc.push_back({});
        dfs_t(u);
    }
    fout << ctc.size() << "\n";
    for(auto& comp : ctc) {
        for(int x : comp)
            fout << x << " ";
        fout << "\n";
    }
    return 0;
}