#include <cstdio>
#include <vector>
#include <deque>
using namespace std;
int n,m;
int in[100023];
vector<int>adj[100023],muc[100023];
deque<int>stiva,sol;
bool viz[500023];
int main()
{
    freopen ("ciclueuler.in","r",stdin);
    freopen ("ciclueuler.out","w",stdout);
    scanf("%d%d",&n,&m);
    int x11,x22;
    for(int i=1;i<=m;i++)
    {
        scanf("%d%d",&x11,&x22);
        adj[x11].push_back(x22);
        muc[x11].push_back(i);
        adj[x22].push_back(x11);
        muc[x22].push_back(i);
        in[x11]++;
        in[x22]++;
    }
    for(int i=1;i<=n;i++)
    {
        if((in[i]&1)==1||(in[i]&1)==1)
        {
            printf("-1");
            return 0;
        }
    }
    stiva.push_back(1);
    while(!stiva.empty())
    {
        int nod=stiva.back();
        if(in[nod]==0)
        {
            stiva.pop_back();
            printf("%d ",nod);
        }
        else
        {
            int x1=adj[nod].back(),x2=muc[nod].back();
            adj[nod].pop_back(),muc[nod].pop_back();
            if(viz[x2]==0)
            {
                viz[x2]=1;
                in[x1]--;
                in[nod]--;
                stiva.push_back(x1);
            }
        }
    }
    return 0;
}