#include <bits/stdc++.h>
using namespace std;
#define LMAX 500001
vector<pair<int,int> > G[LMAX+1];
bool viz[LMAX+1];
int ct=0,ans[LMAX+1];
void Euler(int k){
	while(!G[k].empty()){
        pair<int,int> last=G[k].back();
        G[k].pop_back();
        if(!viz[last.second]){
            viz[last.second]=1;
            Euler(last.first);
        }
	}
	ans[++ct]=k;
}
int main(){
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    int n,m;
    scanf("%d %d",&n,&m);
    for(int i=1;i<=m;++i){
        int u,v;
        scanf("%d %d",&u,&v);
        G[u].push_back({v,i});
        G[v].push_back({u,i});
    }
    for(int i=1;i<=n;++i)
        if(G[i].size()%2==1){
            printf("-1");
            return 0;
        }
    Euler(1);
    for(int i=1;i<ct;++i)
        printf("%d ",ans[i]);
    return 0;
}