#include <cstdio>
#include <algorithm>
#include <vector>
#include <bitset>
#include <stack>

#define Nmax 100005
#define DIM 1666013
#define next (++pointer == DIM) ? fread(buffer,1,DIM,stdin),pointer = 0 : 0

using namespace std;

char buffer[DIM];
int pointer = DIM - 1;

void scanf(int &A){
    A = 0;
    for(;'0'>buffer[pointer]||buffer[pointer]>'9';next);
    for(;'0'<= buffer[pointer]&&buffer[pointer]<='9';next)
        A = A * 10 + buffer[pointer] - 48;
}

vector<int> G[Nmax],Gt[Nmax],ctc[Nmax];
stack<int> S;
bitset<Nmax> used;

int N,M,nc;
void DFS(int nodc)
{
    used[nodc] = 1;
    for(vector<int>::iterator it = G[nodc].begin();it != G[nodc].end(); ++it)
        if(!used[*it]) DFS(*it);
    S.push(nodc);
}
void DFST(int nodc)
{
    used[nodc] = 1;
    ctc[nc].push_back(nodc);
    for(vector<int>::iterator it = Gt[nodc].begin(); it != Gt[nodc].end(); ++it)
        if(!used[*it]) DFST(*it);
}

int main()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);

    scanf(N),scanf(M);
    for(int i = 1; i <= M; ++i){
        int a,b;
        scanf(a),scanf(b);
        G[a].push_back(b);
        Gt[b].push_back(a);
    }

    for(int i = 1; i <= N; ++i)
        if(!used[i])
            DFS(i);
    used = 0;

    while(!S.empty())
    {
        ++nc;
        DFST(S.top());
        while(!S.empty() && used[S.top()])
            S.pop();
    }

    printf("%d\n",nc);
    for(int i = 1; i <= nc; ++i)
    {
        for(vector<int>::iterator it = ctc[i].begin(); it != ctc[i].end(); ++it)
            printf("%d ",*it);
        printf("\n");
    }

    return 0;
}