#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#define maxn 100005
#include <algorithm>
using namespace std;
vector <int> G[maxn];
int n,m,x,y;
stack <int> S;
void Freudy(){
    S.push(1);
    while(!S.empty()){
        x=S.top();
        if(G[x].size()==0){
            printf("%d ",x);
            S.pop();
        }
        else{
            y=*G[x].begin();
            G[x].erase(G[x].begin());
            G[y].erase(find(G[y].begin(),G[y].end(),x));
            S.push(y);
        }
    }
}
int main(){
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;++i){
        scanf("%d%d",&x,&y);
        G[x].push_back(y);
        G[y].push_back(x);
    }
    int ok=1;
    for(int i=1;i<=n;++i)
        if(G[i].size()%2){
            ok=0;
            printf("-1");
            break;
        }
    if(ok)
    Freudy();
    return 0;
}