#include <bits/stdc++.h>
using namespace std;

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

const int MAX_SIZE = 100000;

deque<int> graph[MAX_SIZE + 1];
deque<int> answer;

map<pair<int, int>, bool> visitedEdge;

bool isVisited[MAX_SIZE + 1];

void bfs(deque<int> currentNodes) {
    if (currentNodes.empty() == 1) {
        return;
    }
    deque<int> nextNodes;
    for (deque<int>::iterator it = currentNodes.begin(); it != currentNodes.end(); ++it) {
        for (deque<int>::iterator it2 = graph[*it].begin(); it2 != graph[*it].end(); ++it2) {
            if (isVisited[*it2] == 0) {
                isVisited[*it2] = 1;
                nextNodes.push_back(*it2);
            }
        }
    }
    bfs(nextNodes);
}

void euler(int currentNode) {
    while (graph[currentNode].empty() == 0) {
        if (visitedEdge[{currentNode, graph[currentNode].front()}] == 0) {
            visitedEdge[{currentNode, graph[currentNode].front()}] = 1;
            visitedEdge[{graph[currentNode].front(), currentNode}] = 1;
            int nextNode = graph[currentNode].front();
            graph[currentNode].pop_front();
            euler(nextNode);
        }
    }
    answer.push_back(currentNode);
}

bool isEuler(int noNodes) {
    for (int i = 1; i <= noNodes; ++i) {
        if (graph[i].size() % 2 == 1) {
            return 0;
        }
    }
    deque<int> currentNodes;
    currentNodes.push_back(1);
    isVisited[1] = 1;
    bfs(currentNodes);
    for (int i = 1; i <= noNodes; ++i) {
        if (isVisited[i] == 0) {
            return 0;
        }
    }
    return 1;
}

int main() {
    int noNodes, noEdges;
    fin >> noNodes >> noEdges;
    for (int i = 1; i <= noEdges; ++i) {
        int startNode, endNode;
        fin >> startNode >> endNode;
        graph[startNode].push_back(endNode);
        graph[endNode].push_back(startNode);
    }
    if (isEuler(noNodes) == 0) {
        fout << -1;
    } else {
        euler(1);
        for (int i = 0; i < answer.size(); ++i) {
            fout << answer[i] << ' ';
        }
    }
    return 0;
}