#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#include <queue>

std::ifstream f("ciclueuler.in");
std::ofstream g("ciclueuler.out");

const int NMAX = 1e5;
std::vector<int> L[NMAX + 1];
std::stack<int> st;
std::vector<int> cycle;
int viz[NMAX + 1];

int N, M;

bool isConnected() {
    std::stack<int> dfsStack;
    int visitedCount = 0;

    dfsStack.push(1);
    viz[1] = 1;

    while (!dfsStack.empty()) {
        int current = dfsStack.top();
        dfsStack.pop();
        visitedCount++;

        for (int neighbor : L[current]) {
            if (!viz[neighbor]) {
                viz[neighbor] = 1;
                dfsStack.push(neighbor);
            }
        }
    }

    return visitedCount == N;
}

void findEulerianCycle(int start) {
    st.push(start);

    while (!st.empty()) {
        int current = st.top();

        if (!L[current].empty()) {
            int next = L[current].back();
            L[current].pop_back();

            for (auto it = L[next].begin(); it != L[next].end(); ++it) {
                if (*it == current) {
                    L[next].erase(it);
                    break;
                }
            }

            st.push(next);
        }
        else {
            cycle.push_back(current);
            st.pop();
        }
    }
}

int main() {
    f >> N >> M;

    for (int i = 1; i <= M; ++i) {
        int x, y;
        f >> x >> y;
        L[x].push_back(y);
        L[y].push_back(x);
    }

    for (int i = 1; i <= N; ++i) {
        if (L[i].size() % 2 != 0) {
            g << -1;
            return 0;
        }
    }

    if (!isConnected()) {
        g << -1;
        return 0;
    }

    findEulerianCycle(1);

    for (auto it = cycle.rbegin(); it != cycle.rend(); ++it) {
        g << *it << " ";
    }

    return 0;
}