#include <bits/stdc++.h>

using namespace std;

vector <pair <int, int>> graph[100005];
int where[100005];
int degree[100005];
bitset<500005> visited;
int ansSize;
int answer[500005];

bool isVisited(int index) {
    return visited[index];
}

void visit(int index) {
    visited[index] = true;
}

void dfs(int node) {
    for (int i = where[node]; i < graph[node].size(); ++i) {
        where[node] += 1;
        if (isVisited(graph[node][i].second)) continue;
        visit(graph[node][i].second);
        dfs(graph[node][i].first);
        answer[ansSize++] = graph[node][i].first;
    }
}

int main() {
    ifstream fin ("ciclueuler.in");
    ofstream fout ("ciclueuler.out");
    ios::sync_with_stdio(false);
    fin.tie(nullptr);
    fout.tie(nullptr);
    int n, m;
    fin >> n >> m;
    for (int i = 1; i <= m; ++i) {
        int x, y;
        fin >> x >> y;
        graph[x].emplace_back(y, i);
        graph[y].emplace_back(x, i);
        degree[x] += 1;
        degree[y] += 1;
    }
    for (int i = 1; i <= n; ++i) {
        if (degree[i] == 0 or degree[i] % 2 == 1) {
            fout << -1;
            return 0;
        }
    }
    dfs(1);
    if (ansSize != m) {
        fout << -1;
        return 0;
    }
    for (int i = 0; i < ansSize; ++i) {
        fout << answer[i] << ' ';
    }
    return 0;
}