#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;

ifstream fin ("ciclueuler.in");
ofstream fout ("ciclueuler.out");

const int maxn = 1e5 + 5;
const int maxm = 5e5 + 5;
vector <int> G[maxn];
int Stk[maxm], top;

void Euler () {
    int node, son;
    Stk[++top] = 1;
    while (top > 0) {
        node = Stk[top];
        while (G[node].size() > 0) {
            son = G[node][0];
            G[node].erase(G[node].begin());
            G[son].erase(find(G[son].begin(), G[son].end(), node));
            Stk[++top] = son;
            node = son;
        }
        fout << Stk[top--] << ' ';
    }
}

int main() {
    ios_base :: sync_with_stdio (false);
    int n, m, x, y, i;
    fin >> n >> m;
    for (i = 1; i <= m; i++) {
        fin >> x >> y;
        G[x].push_back(y);
        G[y].push_back(x);
    }
    for (i = 1; i <= n; i++) {
        if (G[i].size() & 1) {
            fout << -1;
            return 0;
        }
    }
    Euler();
    return 0;
}