#include<cstdio>
#include<vector>
#include<queue>
#include<cstring>
using namespace std;
int n,m,e,x,y,i,k;
int viz[500],L[500],R[500],unu[500],doi[500];
vector<int>v[500];
int cupleaza(int s)
{
    int i;
    viz[s]=1;
    for (i=0;i<v[s].size();++i)
    {
        int nod=v[s][i];
        if (R[nod]==0)
        {
            L[s]=nod;
            R[nod]=s;
            return 1;
        }
    }
    for (i=0;i<v[s].size();++i)
    {
        int nod=v[s][i];
        if (viz[R[nod]]==0 && cupleaza(R[nod]))
        {
            L[s]=nod;
            R[nod]=s;
            return 1;
        }
    }
    return 0;
}
void  afis()
{
    int lant=0 ;
    for (int i=1;i<=n;++i)
        if (R[i]==0)
        {
            int nod=i;
            while (L[nod])
                nod=L[nod];
            ++lant;
            unu[lant]=nod;
            doi[lant]=i;
        }
    printf("%d\n",--lant);
    for (int i=1;i<=lant;++i)
    {
        printf("%d %d\n",doi[i],unu[i+1]);
        R[doi[i]]=unu[i+1];
    }
    int start=unu[1];
    while (start)
    {
        printf("%d ",start);
        start=R[start];
    }
}
int main()
{
    freopen("strazi.in","r",stdin);
    freopen("strazi.out","w",stdout);
    scanf("%d%d",&n,&m);
    for (i=1;i<=m;++i)
    {
        scanf("%d%d",&x,&y);
        v[y].push_back(x);
    }
    int ok=0;
    do
    {
        ok=0;
        memset(viz,0,sizeof(viz));
        for (i=1;i<=n;++i)
            if (L[i]==0 && cupleaza(i)) ok=1;
    }while (ok==1);
    afis();
    return 0;
}