# include <fstream>
# include <vector>
# include <cstring>
using namespace std;
ifstream fin("strazi.in");
ofstream fout("strazi.out");
vector<int> Lista[260];
int l[260],r[260],t[260],Marcat[260],n,m,i,j,x,y,ok,nr,ra,rb;
int rad(int nod){
    while(t[nod]>0)
        nod=t[nod];
    return nod;
}
int cuplaj(int nc){
    if(Marcat[nc])
        return 0;
    Marcat[nc]=1;
    for(int i=0;i<Lista[nc].size();i++){
        int nv=Lista[nc][i];
        if(l[nv]==0){
            r[nc]=nv;
            l[nv]=nc;
            return 1;
        }
    }
    for(int i=0;i<Lista[nc].size();i++){
        int nv=Lista[nc][i];
        if(cuplaj(l[nv])){
            r[nc]=nv;
            l[nv]=nc;
            return 1;
        }
    }
    return 0;
}
int main () {
    fin>>n>>m;
    for(i=1;i<=m;i++){
        fin>>x>>y;
        Lista[x].push_back(y);
    }
    ok=1;
    while(ok){
        ok=0;
        memset(Marcat,0,sizeof(Marcat));
        for(i=1;i<=n;i++)
            if(r[i]==0)
                ok=max(ok,cuplaj(i));
    }
    nr=-1;
    for(i=1;i<=n;i++){
        t[i]=-1;
        if(r[i]==0)
            nr++;
    }
    fout<<nr<<"\n";
    for(i=1;i<=n;i++)
        if(l[i]==0)
            for(j=r[i];j!=0;j=r[j]){
                t[i]--;
                t[j]=i;
            }
    for(i=1;i<=n;i++)
        if(r[i]==0)
            for(j=1;j<=n;j++)
                if(rad(i)!=rad(j)&&l[j]==0){
                    ra=rad(i);
                    rb=rad(j);
                    t[ra]+=t[rb];
                    t[rb]=ra;
                    r[i]=j;
                    l[j]=i;
                    fout<<i<<" "<<j<<"\n";
                    j=n+1;
                }
    for(i=1;i<=n;i++)
        if(l[i]==0){
            for(j=i;j!=0;j=r[j])
                fout<<j<<" ";
            fout<<"\n";
            return 0;
        }
    return 0;
}