#include <bits/stdc++.h>
using namespace std;
ifstream fin ("plan.in");
ofstream fout ("plan.out");

const int MAXN=200010;

stack <int> st;
vector <int> g[MAXN],gt[MAXN],componenta[MAXN],radacini,frunze;
bool visitp[MAXN],visitfin[MAXN];
int n,m,rez,compnod[MAXN],inter[MAXN],exter[MAXN],a[MAXN];

void dfs (int nod){
    visitp[nod]=1;
    for (int i=0;i<g[nod].size ();++i){
        if (visitp[g[nod][i]]==0)
            dfs (g[nod][i]);
    }
    st.push (nod);
}
void dfs2 (int nod){
    visitfin[nod]=1;
    compnod[nod]=rez;
    componenta[rez].push_back (nod);
    for (int i=0;i<gt[nod].size ();++i){
        if (visitp[gt[nod][i]]==1 and visitfin[gt[nod][i]]==0){
            dfs2 (gt[nod][i]);
        }
    }
}

void solve (int radacina){
    dfs (radacina);
    while (st.empty ()==false){
        rez++;
        a[rez]=st.top ();
        dfs2 (st.top ());
        while (st.empty ()==false and visitfin[st.top ()]==1)
            st.pop ();
    }
}


int main()
{
    fin >>n>>m;
    for (int i=1;i<=m;++i){
        int x,y;
        fin >>x>>y;
        g[x].push_back (y);
        gt[y].push_back (x);
    }
    for (int i=1;i<=n;++i){
        if (visitfin[i]==0){
            solve (i);
        }
    }
    if (rez==1){
        fout <<0;
        return 0;
    }
    for (int i=1;i<=rez;++i){
        for (int j=0;j<componenta[i].size ();++j){
            int nodcrt=componenta[i][j];
            for (int k=0;k<g[nodcrt].size ();++k){
                int nextn=g[nodcrt][k];
                if (compnod[nextn]!=i){
                    inter[compnod[nextn]]++;
                    exter[i]++;
                }
            }
        }
    }

    for (int i=1;i<=rez;++i){
        if (exter[i]==0)
            frunze.push_back (a[i]);
        if (inter[i]==0)
            radacini.push_back (a[i]);
    }

    fout <<max (frunze.size (),radacini.size ())<<'\n';
    if (frunze.size ()>radacini.size ()){
        for (int i=0;i<radacini.size ();++i)
            fout <<frunze[i]<<' '<<radacini[i]<<'\n';
        for (int i=radacini.size ();i<frunze.size ();++i)
            fout <<frunze[i]<<' '<<radacini.back ()<<'\n';
    }
    else{
        for (int i=0;i<frunze.size ();++i)
            fout <<frunze[i]<<' '<<radacini[i]<<'\n';
        for (int i=frunze.size ();i<radacini.size ();++i)
            fout <<frunze.back ()<<' '<<radacini[i]<<'\n';
    }
    fin.close ();
    fout.close ();
    return 0;
}