#include <bits/stdc++.h>

using namespace std;

const int maxn = 5 + 1e5;

int N, M;
vector <int> v[maxn], inv[maxn];
bool viz[maxn];
vector <int> sol;
int ctc;
vector <int> ans[maxn];

void topologic(int nod)  {
    if(viz[nod])
        return;
    viz[nod] = 1;
    for(auto x : v[nod])
        topologic(x);
    sol.push_back(nod);
}

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

int main()  {
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);
    cin >> N >> M;
    for(int i = 1;i <= M;i++)  {
        int x, y;
        cin >> x >> y;
        v[x].push_back(y);
        inv[y].push_back(x);
    }
    for(int i = 1;i <= N;i++)
        topologic(i);
    for(int i = sol.size() - 1;i >= 0;i--)
        if(viz[sol[i]])  {
            dfs(sol[i]);
            ctc++;
        }
    printf("%d\n", ctc);
    for(int i = 0;i < ctc;i++)  {
        for(int j = 0;j < ans[i].size();j++)
            printf("%d ", ans[i][j]);
        printf("\n");
    }
    return 0;
}