#include <bits/stdc++.h>
#define STOP fout.close(); exit(0);
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
///***********************
const int NMAX = 1e5 + 3, MMAX = 5e5 + 3;
int n, m;
#define fi first
#define se second
vector<pair<int, int>> edges[NMAX];
vector<int> ans;
bitset<MMAX> vis;

void read() {
    fin >> n >> m;
    for (int a, b, i = 1; i <= m; i++) {
        fin >> a >> b;
        edges[a].push_back(make_pair(b, i));
        edges[b].push_back(make_pair(a, i));
    }
}

void dfs(int node) {
    while (!edges[node].empty()) {
        int to, nrEdge;
        tie(to, nrEdge) = edges[node].back();
        edges[node].pop_back();
        if (!vis[nrEdge]) {
            vis[nrEdge] = true;
            dfs(to);
        }
    }
    ans.push_back(node);
}

int main() {
    read();
    for (int i = 1; i <= n; i++)
        if (edges[i].size() & 1)
            return fout << -1 << endl, 0;
    dfs(1);
    for (int i = 0; i < m; i++)
        fout << ans[i] << ' ';
    STOP
}