#include <bits/stdc++.h>

using namespace std;
ofstream fout("ctc.out");
ifstream fin("ctc.in");


const int NMax = 100010;
vector<vector<int> > ans;
vector<int> G[NMax];

int d[NMax];
int low[NMax];
stack<int> st;
bool onstack[NMax];
int n, m, x, y;
int indexi;

void dfs(int node){
    d[node] = ++indexi;
    low[node] = indexi;
    onstack[node] = true;
    st.push(node);
    indexi++;

    for(auto next : G[node]){
        if(!d[next]) dfs(next), low[node] = min(low[node], low[next]);
        else if(onstack[next])  low[node] = min(low[node], low[next]);
    }

    if(d[node] == low[node]){
        ans.push_back(vector<int>());

        int v;
        do{
            v = st.top();
            ans[ans.size() - 1].push_back(v);
            onstack[v] = false;
            st.pop();
        }while(v != node);
    }
}

int main()
{
    fin >> n >> m;

    for(int i = 1; i <= m; i++){
        fin >> x >> y;
        G[x].push_back(y);
    }

    for(int i = 1; i <= n; i++){
        if(d[i] == 0)
            dfs(i);
    }

    fout << ans.size()<< '\n';

    for(int i = 0; i < ans.size(); i++){
        for(int j = 0; j < ans[i].size(); j++){
            fout << ans[i][j] << ' ';
        }

        fout << '\n';
    }

    return 0;
}