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

int n, m, i, j, x, y, nrc, ctc[100002];
bool plus[100002], minus[100002];
vector<int>G[100002], GT[100002];
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]);
}
void dfs2 (int x)
{
    minus[x]=1;
    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 (ctc[i]==0){
            memset(plus, 0, n+1);
            memset(minus, 0, n+1);
            nrc++;
            dfs1(i);
            dfs2(i);
            for (int j=1; j<=n; j++)
                if (plus[j]==1 && minus[j]==1) ctc[j]=nrc;
        }
    }
    printf("%d\n", nrc);
    for (i=1; i<=nrc; i++){
        for (j=1; j<=n; j++)
            if (ctc[j]==i) printf("%d ", j);
        printf("\n");
    }
    return 0;
}