#include<fstream>
#include<sstream>
#include<vector>
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
ostringstream sout;
vector <int> v[100001];
vector <int> vt[100001];
int n, m, i, j, a, b, k, nr;
int viz[100001];
int postord[100001];

void dfst(int nod){
    viz[nod] = 0; int i; sout << nod << " ";
    for (i = 0; i < vt[nod].size(); i++)
        if (viz[vt[nod][i]] == 1)
            dfst(vt[nod][i]);
}

void dfs(int nod){
    viz[nod] = 1; int i;
    for (i = 0; i < v[nod].size(); i++)
        if (!viz[v[nod][i]])
            dfs(v[nod][i]);
    postord[++nr] = nod;
}

int main(){
    fin >> n >> m;
    for (i = 1; i <= m; i++){
        fin >> a >> b;
        v[a].push_back(b);
        vt[b].push_back(a);
    }
    for (i = 1; i <= n; i++)
        if (!viz[i])
            dfs(i);
    for (i = n; i >= 1; i--){
        if (viz[postord[i]] == 1){
            k++;
            dfst(postord[i]);
            sout << '\n';
        }
    }
    fout << k << '\n';
    fout << sout.str();
    fin.close();
    fout.close();
}