#include <bits/stdc++.h>

using namespace std;

const int NMax = 100005;

int n,m,top,ctc_nr,x,y;
int viz[NMax],grad[NMax];
multiset<int> G[NMax];
stack<int> st;

int main(){
    ifstream cin("ciclueuler.in");
    ofstream cout("ciclueuler.out");
    cin >> n >> m;
    for(int i = 1; i <= m; ++i){
        cin >> x >> y;
        G[x].insert(y);
        G[y].insert(x);
        grad[x]++;
        grad[y]++;
    }
    for(int i = 1; i <= n; ++i){
        if(grad[i] % 2 != 0){
            cout << -1 << '\n';
            return 0;
        }
    }
    st.push(1);
    int nr = 0;
    while(!st.empty()){
        int curr = st.top();
        if(G[curr].size() == 0){
            if(nr++ >= m){
                return 0;
            }
            cout << curr << ' ';
            st.pop();
        }else{
            int nei = (*G[curr].begin());
            auto nei_iter = G[curr].begin();
            G[curr].erase(nei_iter);
            auto curr_iter_in_nei = G[nei].find(curr);
            G[nei].erase(curr_iter_in_nei);
            st.push(nei);
        }
    }

    return 0;
}