#include <bits/stdc++.h>

using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");
vector <int> v[100005];
vector <int> c[100005];
int viz[100005];
int res[100005];
vector <int> rez[100005];
int contor;
int cnt = 0;
void f(int x)
{
    viz[x] = 1;
    for(auto it : v[x])
        if(viz[it] == 0)
            f(it);
    res[cnt] = x;
    cnt ++;
}

void f2(int x)
{
    viz[x] = 1;
    rez[contor].push_back(x);
    for(auto it : c[x])
        if(viz[it] == 0)
            f2(it);
}

int main()
{
    int n, m;
    in >> n >> m;
    for(int i = 1; i <= m; i ++)
    {
        int a, b;
        in >> a >> b;
        v[a].push_back(b);
        c[b].push_back(a);
    }
    for(int i = 1; i <= n; i ++)
        if(viz[i] == 0)
            f(i);
    for(int i = 1; i <= n; i ++)
        viz[i] = 0;
    for(int i = cnt - 1; i >= 0; i --)
    {
        int x = res[i];
        if(viz[x] == 0)
        {
            f2(x);
            contor ++;
        }
    }
    out << contor << '\n';
    for(int i = 0; i < contor; i ++)
    {
        for(auto it : rez[i])
            out << it << " ";
        out << '\n';
    }
    return 0;
}