#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <string>
#include <queue>
#include <bitset>
using namespace std;
const string fileName="ctc";
ifstream in (fileName+".in");
ofstream out(fileName+".out");
const int nmax=1e5;
int n, m;
vector <int> muchii[nmax+2];
int low[nmax+2];
int x, y;
bool onStack[nmax+2];
int tin[nmax+2];
vector <vector <int> > comp;
vector <int> stk;
int mom;
int partComp[nmax+2];
void dfs(int nod){
    stk.push_back(nod);
    onStack[nod]=true;
    low[nod]=tin[nod]=++mom;
    for(auto &x:muchii[nod]){
        if(onStack[x]){
            low[nod]=min(low[nod], tin[x]);
        }
        else if(tin[x]==0){ ///adica nu e pe stiva si nici nu a fost parcurs
            dfs(x);
            low[nod]=min(low[nod], low[x]);
        }
    }
    if(low[nod]>=tin[nod]){
        comp.push_back(vector<int>());
        while(!stk.empty()&&stk.back()!=nod){
            comp.back().push_back(stk.back());
            partComp[stk.back()]=comp.size();
            onStack[stk.back()]=false;
            stk.pop_back();
        }
        comp.back().push_back(nod);
        partComp[stk.back()]=comp.size();
        onStack[stk.back()]=false;
        stk.pop_back();
    }
}
ostream & operator << (ostream & out, pair<int, int> & per){
    out<<per.first<<" "<<per.second;
    return out;
}
template <typename T>
ostream & operator << (ostream & out, vector <T> & vec){
    for(auto &x:vec)
        out<<x<<" ";
    return out;
}
vector <pair <int, int> > sol;
int main()
{
    in>>n>>m;
    for(int i=1; i<=m; i++){
        in>>x>>y;
        muchii[x].push_back(y);
    }
    for(int i=1; i<=n; i++)
        if(tin[i]==0)
            dfs(i);

    out<<comp.size()<<"\n";
    for(auto &x:comp)
        out<<x<<"\n";

    /*for(int i=1; i<=n; i++){
        for(auto &x:muchii[i])
            if(partComp[x]!=partComp[i]){
                sol.push_back({i, x});
            }
    }
    sort(sol.begin(), sol.end());
    cout<<sol.size()<<"\n"<<sol;*/

    /*out<<comp.size()<<"\n";
    for(auto &x:comp)
        out<<x<<"\n";*/
    return 0;
}