#include <bits/stdc++.h>

using namespace std;

const int nmax = 1e5 + 10;
const int mmax = 5e5 + 10;

int n, m;
int last, st[mmax], used[mmax];
pair < int, int > edge[mmax];
vector < int > g[nmax], ans;

void input() {
    scanf("%d %d", &n, &m);
    for (int i = 1; i <= m; ++i) {
        int x, y;
        scanf("%d %d", &x, &y);

        g[x].push_back(i);
        g[y].push_back(i);

        edge[i] = {x, y};
    }
}

void no_solution() {
    printf("-1\n");
    exit(0);
}

int second_node(int idx, int node) {
    return (edge[idx].first == node) ? edge[idx].second : edge[idx].first;
}

void run_euler() {
    for (int i = 1; i <= n; ++i)
        if ((int)g[i].size()&1)
            no_solution();

    st[++last] = 1;
    while (last) {
        int node = st[last];

        if (g[node].size() == 0)
            ans.push_back(node), last--;
        else {
            int curr = g[node].back(); g[node].pop_back();
            if (used[curr]) continue;

            used[curr] = 1;
            st[++last] = second_node(curr, node);
        }
    }
    ans.pop_back();
}

void output() {
    for (auto &it: ans)
        printf("%d\n", it);
}

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

    input();
    run_euler();
    output();

    return 0;
}