#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
const int MAXN = 1e5 + 5;
vector <pair<int, int>> v[MAXN];
bool seen[MAXN];
int m;
void dfs(int node){
    while(v[node].size()){
        int current = v[node].back().first;
        int indice = v[node].back().second;
        v[node].pop_back();
        if(!seen[indice]){
            seen[indice] = true;
            dfs(current);
        }
    }
    if(m) fout << node << " " , m--;
}
int main(){
    int n; fin >> n >> m;
    for(int i = 1; i <= m; ++i){
        int x, y; fin >> x >> y;
        v[x].push_back({y, i});
        v[y].push_back({x, i});
    }
    for(int i = 1; i <= n; ++i){
        if(v[i].size() % 2){
            fout << "-1";
            return 0;
        }
    }
    dfs(1);
    return 0;
}