#include <bits/stdc++.h>

using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
const int nMax = 100003;
vector <int> Graf[nMax];
bool viz[nMax];
int ans[nMax], st[nMax], dr[nMax];
int n, m, k;
inline bool Euler() {
    for(int i = 1; i <= n; i++) {
        if(Graf[i].size() & 1) {
            return 0;
        }
    }
    return 1;
}
inline void Dfs(int nod) {
    for(const auto &i : Graf[nod]) {
        if(!viz[i]) {
            viz[i] = 1;
            Dfs(st[i] + dr[i] - nod);
        }
    }
    ans[++k] = nod;
}
int main()
{
    f >> n >> m;
    for(int i = 1; i <= m; i++) {
        f >> st[i] >> dr[i];
        Graf[st[i]].push_back(i);
        Graf[dr[i]].push_back(i);
    }
    if(!Euler()) {
        g << "-1\n";
        return 0;
    }
    Dfs(1);
    for(int i = 1; i <= k; i++) {
        g << ans[i] << " ";
    }
    return 0;
}