#include<cstdio>
#include<vector>
using namespace std;
vector<int>L[300];
int n,m,i,j,nr,ok,a,b,v[300],x[300][300],y[300],l[300],r[300];
FILE *f,*g;
int cupl(int nod){
    if(v[nod]==1)
        return 0;
    v[nod]=1;
    for(int i=0;i<L[nod].size();i++){
        if( l[ L[nod][i] ] == 0 || cupl( l[ L[nod][i] ] )  ){
            r[nod]=L[nod][i];
            l[ L[nod][i] ]=nod;
            return 1;
        }
    }
    return 0;
}
void fct(int nod){
    y[++nr]=nod;
    if(r[nod])
        fct(r[nod]);
}
int main(){
    f=fopen("strazi.in","r");
    g=fopen("strazi.out","w");
    fscanf(f,"%d%d",&n,&m);
    for(i=1;i<=m;i++){
        fscanf(f,"%d%d",&a,&b);
        L[a].push_back(b);
        x[a][b]=1;
    }
    nr=0;
    ok=1;
    while(ok){
        ok=0;
        for(i=1;i<=n;i++){
            v[i]=0;
        }
        for(i=1;i<=n;i++){
            if(r[i]==0&&cupl(i)){
                nr++;
                ok=1;
            }
        }
    }
    fprintf(g,"%d\n",n-nr-1);
    nr=0;
    for(i=1;i<=n;i++){
        if(l[i]==0)
            fct(i);
    }
    for(i=1;i<nr;i++){
        if( x[ y[i] ][ y[i+1] ] == 0 )
            fprintf(g,"%d %d\n",y[i],y[i+1]);
    }
    for(i=1;i<=n;i++){
        fprintf(g,"%d ",y[i]);
    }
    fclose(f);
    fclose(g);
    return 0;
}