#include <cstdio>
#include <vector>
#include <stack>
using namespace std;

int n, m, i, j, x, y, nrc, k;
int plus[100002], minus[100002];
vector<int>G[100002], GT[100002], ctc[100002];
stack<int>st;
void dfs1 (int x)
{
    plus[x]=1;
    for (int i=0; i<G[x].size(); i++)
        if (plus[G[x][i]]==0) dfs1(G[x][i]);
    st.push(x);
}
void dfs2 (int x)
{
    minus[x]=nrc;
    for (int i=0; i<GT[x].size(); i++)
        if (minus[GT[x][i]]==0) dfs2(GT[x][i]);
}
int main ()
{
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);

    scanf("%d%d", &n, &m);

    for (i=1; i<=m; i++){
        scanf("%d%d", &x, &y);
        G[x].push_back(y);
        GT[y].push_back(x);
    }
    for (i=1; i<=n; i++){
        if (plus[i]==0) dfs1(i);
    }
    while (!st.empty()){
        k=st.top();
        st.pop();
        if (minus[k]==0){
            nrc++;
            dfs2(k);
        }
    }
    for (i=1; i<=n; i++)
        ctc[minus[i]].push_back(i);

    printf("%d\n", nrc);
    for (i=1; i<=nrc; i++){
        for (j=0; j<ctc[i].size(); j++)
            printf("%d ", ctc[i][j]);
        printf("\n");
    }
    return 0;
}