#include<cstdio>
#include<vector>
using namespace std;
int n,m,ok,stv[500010],h,el;
vector<int>v[100010];
void citire()
{
    int x,y;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++)
    {
        scanf("%d%d",&x,&y);
        v[x].push_back(y);
        v[y].push_back(x);
    }
    ok=0;
    for(int i=1;i<=n;i++)
        if(v[i].size()%2!=0)
        {
            ok=-1;
            break;
        }
}
int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);

    citire();int x;
    if(ok==-1)
        printf("%d",ok);
    else
    {
        stv[1]=1;
        h=1;
        while(h!=0)
        {
            x=stv[h];
            if(!v[x].empty())
            {
                stv[++h]=v[x][0];
                el=v[x][0];
                v[x][0]=v[x].back();
                v[x].pop_back();
                for(int i=0;i<v[el].size();i++)
                {
                    if(v[el][i]==x)
                    {
                        v[el][i]=v[el].back();
                        v[el].pop_back();
                        break;
                    }
                }
            }
            else
            {
                while(h!=0 && v[stv[h]].empty())
               {
                   printf("%d ",stv[h]);
                    h--;
               }
            }
        }
    }
}