#include <stdio.h>
#include <vector>
#include <list>
#include <bitset>
#define NMAX 100005

using namespace std;

vector <int> G[NMAX];
list <int> L;
bitset <NMAX> viz;
int N, M, grad[NMAX];

void dfs(int nod){
    viz[nod] = 1;
    for(vector <int> :: iterator it = G[nod].begin(); it != G[nod].end(); ++it)
        if(!viz[*it])
            dfs(*it);

}

int main(){
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    int x, y, ok = 1, nod;
    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);
        ++grad[x];
        ++grad[y];
    }
    dfs(1);
    for(int i = 1; i <= N; ++i){
        if(!viz[i]){
           printf("-1\n");
           ok = 0;
           break;
        }
        if(grad[i] % 2){
            printf("-1\n");
            ok = 0;
            break;
        }
    }
    if(ok){
        L.push_back(1);
        while(!L.empty()){
            nod = L.front();
            if(G[nod].empty()){
                printf("%d ", nod);
                L.pop_front();
            }else{
                int i = G[nod].back();
                L.push_front(i);
                G[nod].pop_back();
                for(vector <int> :: iterator it = G[i].begin(); it != G[i].end(); ++it)
                    if(*it == nod){
                        G[i].erase(it);
                        break;
                    }
            }
        }
    }
    return 0;
}