#include <cstdio>
#include <vector>
using namespace std;
int i, x, y, N, M, nr, Sel[100001];
vector<int> G[100001],Gt[100001],Sol[100001],Stiva;
inline void DF(int);
inline void DF2(int);
int main()
{
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);
    scanf("%d%d", &N, &M);
    for (i=1; i<=N; i++)
    {
        scanf("%d%d", &x, &y);
        G[x].push_back(y);
        Gt[y].push_back(x);
    }
    for (i=1; i<=N; i++)
        if (!Sel[i]) DF(i);
    for (i=1; i<=N; i++)
        Sel[i]=0;
    for (i=0; i<Stiva.size(); i++)
        if (!Sel[Stiva[i]])
        {
            nr++;
            DF2(Stiva[i]);
        }
    printf("%d\n", nr);
    for (i=1; i<=nr; i++)
    {
        for (vector<int>::iterator it=Sol[i].begin(); it!=Sol[i].end(); it++)
            printf("%d ", *it);
        printf("\n");
    }
}
inline void DF(int x)
{
    Sel[x]=1;
    for (vector<int>::iterator it=G[x].begin(); it!=G[x].end(); it++)
        if (!Sel[*it]) DF(*it);
    Stiva.push_back(x);
}
inline void DF2(int x)
{
    Sel[x]=1;
    for (vector<int>::iterator it=Gt[x].begin(); it!=Gt[x].end(); it++)
        if (!Sel[*it]) DF2(*it);
    Sol[nr].push_back(x);
}