#include <fstream>
#include <vector>
#include <bitset>
#define DIM 10002

using namespace std;

ifstream fin("strazi.in");
ofstream fout("strazi.out");

vector <int> v[DIM], S[DIM];
int N, M, E, ok, nr, k;
int L[DIM], R[DIM];
bitset <DIM> u;
// L[i] = nodul din dreapta cu care este cuplat momentan noul i din stanga
// R[i] = nodul din stanga cu care este cuplat momentan noul i din dreapta

int cupleaza(int nod /*din stanga*/) {
    if (u[nod])
        return 0;
    u[nod] = 1;
    // incerc sa cuplez pe nod cu un nod liber
    for (vector<int>::iterator it = v[nod].begin(); it != v[nod].end(); it++) {
        if (R[*it] == 0) {
            L[nod] = *it;
            R[*it] = nod;
            return 1;
        }
    }

    for (vector<int>::iterator it = v[nod].begin(); it != v[nod].end(); it++) {
        if ( cupleaza( R[*it] )) {
            L[nod] = *it;
            R[*it] = nod;
            return 1;
        }
    }
    return 0;

}


int main () {

    fin >> N >> E;

    while(E--){
        int x,y;
        fin >> x >> y;
        v[x].push_back(y);
    }

    do {
        u.reset();
        ok = 0;
        for(int i=1;i<=N;i++)
            if(!L[i]) {
                ok = ok | cupleaza(i);
            }

    } while (ok);

    for(int i=1;i<=N;i++)
        if(L[i])
            nr++;
/*
    fout << nr << "\n";

    for(int i=1;i<=N;i++)
        if(L[i])
            fout << i << " " << L[i] << "\n";
*/
    u.reset();

    for (int i=1;i<=N;i++)
        if (L[i] != 0 && u[i] == 0 && R[i] == 0) {
            // in i incepe un lant
            ++k;
            int j = i;
            S[k].push_back(j);
            u[j] = 1;
            while (L[j] != 0) {
                S[k].push_back(L[j]);
                j = L[j];
                u[j] = 1;
            }
        }
    /*
    fout << "\n";
    fout << k << "\n";
    */

    fout<<k<<"\n";
    for (int i=1;i<k;i++)
        fout<<S[i][ S[i].size() -1 ] <<" "<<S[i+1][0]<<"\n";
    fout<<S[k][ S[k].size() -1 ]<<" "<<S[1][0]<<"\n";

    for (int i=1;i<=k;i++) {
        for (int j=0;j<S[i].size();j++)
            fout<<S[i][j]<<" ";
    }




    return 0;
}