#include <bits/stdc++.h>

using namespace std;

const int maxn = 100000, maxm = 200000;

int N, M;
vector <int> v[maxn + 1], inv[maxn + 1];
int topo[maxn + 1];
vector <int> sol[maxn + 1];
int ans, ind;
bool viz[maxn + 1];

void dfs_sort_top(int nod)  {
    if(viz[nod])
        return;
    viz[nod] = 1;
    for(auto &x : v[nod])  {
        dfs_sort_top(x);
    }
    topo[++ind] = nod;
}

void dfsinv(int nod)  {
    if(!viz[nod])
        return;
    viz[nod] = 0;
    for(auto &x : inv[nod])  {
        dfsinv(x);
    }
    sol[ans].push_back(nod);
}

inline int read()  {
    char ch = getchar();int x = 0;
    while(!isdigit(ch)) ch = getchar();
    while(isdigit(ch)) x = x * 10 + ch - '0', ch = getchar();
    return x;
}

int main()  {
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);
    N = read(), M = read();
    for(int i = 0;i < M;i++)  {
        int x, y;
        x = read(), y = read();
        v[x].push_back(y);
        inv[y].push_back(x);
    }
    for(int i = 1;i <= N;i++)
        dfs_sort_top(i);
    for(int i = N;i >= 1;i--)  {
        if(viz[topo[i]])  {
            dfsinv(topo[i]);
            ans++;
        }
    }
    cout << ans << "\n";
    for(unsigned int i = 0;i < ans;i++)  {
        for(auto &x : sol[i])
            cout << x << " ";
        cout << "\n";
    }
    return 0;
}