#include <bits/stdc++.h>
using namespace std;
int n,m,x,y,ap[100001],nr,apPlus[100001],apMinus[100001],nrc;

void date()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);
}
vector <int> G[100001],GT[100001],rez[100001];
stack <int> st;
void dfsPlus(int x)
{
    apPlus[x]=1;
    for(int i=0;i<G[x].size();i++)
        if(apPlus[G[x][i]]==0)
            dfsPlus(G[x][i]);
    st.push(x);

}
void dfsMinus(int x)
{
    apMinus[x]=nrc;
    for(int i=0;i<GT[x].size();i++)
        if(apMinus[GT[x][i]]==0)
            dfsMinus(GT[x][i]);

}
int main()
{
    date();
    scanf("%d%d",&n,&m);
    while(m--)
    {
        scanf("%d%d",&x,&y);
        G[x].push_back(y);
        GT[y].push_back(x);

    }

    for(int i=1;i<=n;i++)
        if(apPlus[i] == 0)
            dfsPlus(i);
    while(!st.empty())
    {
        x=st.top();
        st.pop();
        if(apMinus[x] == 0)
        {
            nrc++;
            dfsMinus(x);
        }
    }
    for(int i=1;i<=n;i++)
        rez[apMinus[i]].push_back(i);
    printf("%d\n",nrc);
    for(int i=1;i<=nrc;i++){
        for(int j=0;j<rez[i].size();j++)
            printf("%d ",rez[i][j]);
        printf("\n");
}

    return 0;
}