#include <bits/stdc++.h>
#include <vector>
#include <stack>
using namespace std;

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

vector <int> a[100001];
vector <int> b[100001];
int viz[100001];

stack <int> st;

int n, m, ct;

void dfs(int nod)
{
    viz[nod] = 1;
    for(auto i:a[nod])
        if(!viz[i])
            dfs(i);
    st.push(nod);
}

void dfs2(int nod)
{
    vf[ct].push_back(nod);
    viz[nod] = 2;
    for(auto i:b[nod])
    {
        if(viz[i] != 2)
            dfs2(i);
    }
}

int main()
{
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        a[x].push_back(y);
        b[y].push_back(x);
    }
    for(int i = 1; i <= n; i++)
    {
        if(!viz[i])
        {
            dfs(i);
        }
    }
    while(!st.empty)
    {
        int c = st.top();
        st.pop();
        if(viz[c] == 1)
            ct++, dfs2(c);
    }
    fout << ct << '\n';
    for(int i = 1; i <= ct; i++)
    {
        for(auto j:vf[i])
            cout << j << " ";
        cout << '\n';
    }
    return 0;
}