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

const int nmx = 100002;

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

void euler() {
    stack <int> s;
    s.push(1);
    while(not s.empty()) {
        int nod = s.top();
        if(g[nod].size()) {
            int fiu = g[nod].back();
            s.push(fiu);
            g[nod].pop_back();
            g[fiu].erase(find(g[fiu].begin(),g[fiu].end(),nod));

        } else {
            printf("%d ", nod);
            s.pop();
        }
    }
}

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

    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[nod1];
        ++ grad[nod2];
    }

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

    euler();
    return 0;
}