#include<cstdio>
#include<vector>
#include<algorithm>
using namespace std;
int n,i,j,m,nrv[100001],cate,vec[500001],q[500001],pp,st[500001],numar;
vector<int> v[100001];
int main ()
{
freopen("ciclueuler.in","r",stdin);
freopen("ciclueuler.out","w",stdout);
scanf("%d%d",&n,&m);
int x,y,poz,maxim=0;
for(i=1;i<=m;i++)
    {
    scanf("%d%d",&x,&y);
    v[x].push_back(y);
    v[y].push_back(x);
    nrv[x]++;
    nrv[y]++;
    }
for(i=1;i<=n;i++)
    if(nrv[i]%2==1)
        pp=1;
if(pp==0)
    {
    st[++cate]=1;
    while(cate!=0)
        {
        y=st[cate];
        x=0;
        if(v[y].size()>=1)
            x=v[y][v[y].size()-1];
        if(x!=0)
            {
            v[y].pop_back();
            st[++cate]=x;
            v[x].erase(find(v[x].begin(),v[x].end(),y));
            }
        else
            {
            if(numar<m)
                printf("%d\n",st[cate]);
            cate--;
            numar++;
            }
        }
    }
else
    printf("-1");
return 0;
}