#include <cstdio>
#include <algorithm>
#include <vector>
#include <stack>
#define NMAX 100005

using namespace std;

int n, m, g, x, y, nr;
int viz[NMAX],niv[NMAX],low[NMAX];

stack<int>st;
vector<int>v[NMAX],sol[NMAX];

void DFS(int nod)
{
    st.push(nod);
    viz[nod]=1;
    niv[nod]=low[nod]=++g;
    for(int i = 0; i < v[nod].size();++i)
    {
        if (niv[v[nod][i]] == 0)
        {
            DFS(v[nod][i]);
            low[nod]=min(low[nod],low[v[nod][i]]);
        }
        else if (viz[v[nod][i]] == 1) low[nod]=min(low[v[nod][i]],low[nod]);

    }

    if (niv[nod] == low[nod])
    {
        ++nr;
        int x;
        do
        {
             x= st.top();
            sol[nr].push_back(x);
            viz[x]=0;
            st.pop();
        }while(x != nod);
    }
}

int main()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);
    scanf("%d%d",&n,&m);
    for(int i = 1; i <= m; ++i)
    {
        scanf("%d%d",&x,&y);
        v[x].push_back(y);
    }

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

    printf("%d\n",nr);
    for(int i = 1; i <= nr; ++i)
    {
        sort(sol[i].begin(),sol[i].end());

        for(int j = 0; j < sol[i].size(); ++j)
            printf("%d ",sol[i][j]);
        printf("\n");
    }
    return 0;
}