#include <iostream>
#include <fstream>
#include <vector>
#include <deque>

using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");

vector<int> gf[100010], gt[100010], ans[100010];
deque<int> coada;
int n, m, x, y, nr, viz[100010], ctc[100010];

void DF1(int nod){
    viz[nod] = 1;
    for(int i = 0; i < gf[nod].size(); ++i){
        int nxt = gf[nod][i];
        if(viz[nxt] == 0){
            DF1(nxt);
        }
    }
    coada.push_front(nod);
}

void DF2(int nod){
    ctc[nod] = nr;
    for(int i = 0; i < gt[nod].size(); ++i){
        int nxt = gt[nod][i];
        if(ctc[nxt] == 0){
            DF2(nxt);
        }
    }
}

int main()
{
    fin >> n >> m;
    for(int i = 1; i <= m; ++i){
        fin >> x >> y;
        gf[x].push_back(y);
        gt[y].push_back(x);
    }
    DF1(1);
    for(auto& it : coada){
        if(ctc[it] == 0){
            nr++;
            DF2(it);
        }
    }
    fout << nr;
    nr = 0;
    for(auto& it : coada){
        if(ctc[it] != nr){
            nr++;
            fout << '\n';
        }
        fout << it << ' ';
    }
    return 0;
}