#include <cstdio>
#include <vector>
#include <stack>
#include <algorithm>

using namespace std;

const int nmx = 100002;

int n,m,grad[nmx];
vector <int> g[nmx];
stack <int> st;

void citire() {
    scanf("%d %d", &n, &m);
    int nod1,nod2;
    for(int i = 1; i <= m; ++i) {
        scanf("%d %d", &nod1, &nod2);
        g[nod1].push_back(nod2);
        g[nod2].push_back(nod1);
        ++ grad[nod2];
        ++ grad[nod1];
    }
}

void euler() {
    st.push(1);
    while(not st.empty()) {
        int nod = st.top();
        if(g[nod].size()) {
            int aux = g[nod].back();
            g[nod].pop_back();
            g[aux].erase(find(g[aux].begin(),g[aux].end(),nod));
            st.push(aux);
        } else {
            printf("%d ", nod);
            st.pop();
        }
    }
}

int main() {
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);

    citire();

    for(int i = 1; i <= n; ++i)
        if(grad[i] % 2) {
            printf("-1\n");
            return 0;
        }

    euler();

    return 0;
}