#include <bits/stdc++.h>

using namespace std;
vector < pair<int, int>> graff[100001];
bool vizitate[500001];
vector <int> sol;
int grad [100100];
void dfs(int nod){
    while (graff[nod].size())
    {
        if (vizitate[graff[nod].back().second]) {
            graff[nod].pop_back();
        }
        else {
            vizitate[graff[nod].back().second] = 1;
            dfs(graff[nod].back().first);
        }
    }
    sol.push_back(nod);
}

int main() {
    ifstream f("ciclueuler.in");
    ofstream g("ciclueuler.out");
    int n, m;
    f >> n >> m;
    for (int i = 1; i <= m; i++) {
        int x, y;
        f >> x >> y;
        graff[x].emplace_back(y, i);
        graff[y].emplace_back(x, i);
        grad[x] += 1;
        grad[y] += 1;
    }
    for (int i = 1; i <= n; ++i)
    {
        if (grad[i] % 2 == 1) {
            g << -1;
            return 0;
        }
    }
    dfs(1);
    for (int i = 1; i <= m; ++i) {
        if (vizitate[i] == 0) {
            g << -1;
            return 0;
        }
    }
    sol.pop_back();
    if(sol.size() != m){
        g << -1;
        return 0;
    }
    for (auto &x : sol)
        g << x << ' ';
    return 0;
}