#include <bits/stdc++.h>
using namespace std;

#define pb push_back

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

const int N = 1e5 + 5;
const int M = 5e5 + 5;

int n, m; 
vector<int> stk, rez, v[N];
vector<pair<int, int>> muchii;
bitset<M> u;

void read(), check(), euler();

int main()
{
    read();
    check();
    euler();
    rez.pop_back();
    for (auto it: rez) g << it << ' ' ;
    
    return 0;
}
void read(){
    f >> n >> m;
    int x, y;
    for (int i = 0; i < m; i++){
        f >> x >> y;
        v[x].pb(i); v[y].pb(i);
        muchii.pb({x, y});
    }
}
void check(){
    for (int i = 1; i <= n; i++)
        if (v[i].size() % 2){
            g << -1; exit(0);
        }
}
void euler(){
    stk.pb(1);
    while (stk.size()){
        int nod = stk.back();
        if (v[nod].size()) {
            int ord = v[nod].back(); v[nod].pop_back();
            if (u[ord]) continue;
            u[ord] = 1;
            int x, y; tie(x, y) = muchii[ord];
            x == nod ? stk.pb(y) : stk.pb(x);
        }
        else {
            stk.pop_back();
            rez.pb(nod);
        }
    }
}