#include <cstdio>
#include <vector>
#include <stack>
#include <algorithm>
#define nmx 100005
using namespace std;

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

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

int main() {
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    scanf("%d %d", &n, &m);
    for(; m; --m) {
        int nod1, nod2;
        scanf("%d %d", &nod1, &nod2);
        g[nod1].push_back(nod2);
        g[nod2].push_back(nod1);
        ++ grad[nod1];
        ++ grad[nod2];
    }
    for(int i = 1; i <= n; ++i)
        if(grad[i] % 2) {
            printf("-1\n");
            return 0;
        }
    euler();
    return 0;
}