#include <bits/stdc++.h>
using namespace std;

#define FOR(i,a,b) for(int i = a; i <= b; i++)
#define ROF(i,a,b) for(int i = a; i >= b; i--)
#define pb push_back

int n,m;
vector<int> G[100001];
vector<int> TG[100001];
int ST[100001];
bool seen[100001];
vector< vector<int> > comp;

void dfs1(int x)
{
    seen[x] = 1;
    FOR(i,0,(int)G[x].size()-1)
        if (!seen[G[x][i]]) 
            dfs1(G[x][i]);
    ST[++ST[0]] = x;
}

void dfs2(int x)
{
    seen[x] = 1;
    comp.back().pb(x);
    FOR(i,0,(int)TG[x].size()-1)
        if (!seen[TG[x][i]])
            dfs2(TG[x][i]);
}

int main()
{
    ifstream fin("ctc.in");
    ofstream fout("ctc.out");

    fin >> n >> m;
    
    FOR(i,1,m)
    {
        int x,y;
        fin >> x >> y;
        G[x].pb(y);
        TG[y].pb(x);
    }

    FOR(i,1,n) if (!seen[i]) dfs1(i);
    fill_n(seen+1,n,0);
    ROF(i,ST[0],1) {
        if (!seen[ST[i]])
        {
            comp.pb(vector<int>());
            dfs2(ST[i]);
        }
    }

    fout << (int)comp.size() << "\n";
    FOR(i,0,(int)comp.size()-1)
    {
        FOR(j,0,(int)comp[i].size()-1)
            fout << comp[i][j] << " ";
        fout << "\n";
    }

}