#include <iostream>
#include <fstream>
#include <vector>
#include <bitset>
using namespace std;

vector<pair<int,int>> graph[100001];
vector<int> euler;
int grad[100001];
bool muchii[500001];

void dfs(int node){
    while(graph[node].size()){
        if(muchii[graph[node].back().second]){
            graph[node].pop_back();
            continue;
        }
        muchii[graph[node].back().second] = 1;
        dfs(graph[node].back().first);
    }
    euler.push_back(node);
}

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

    int n,m;
    fin >> n >> m;
    for(int i = 1;i <= m; ++i){
        int x,y;
        fin >> x >> y;
        graph[x].push_back({y,i});
        graph[y].push_back({x,i});
        grad[x] ^= 1;
        grad[y] ^= 1;
    }

    for(int i = 1;i <= n; ++i){
        if(grad[i]){
            fout << -1;
            return 0;
        }
    }

    dfs(1);

    euler.pop_back();
    if(euler.size()!=m){
        fout << -1;
        return 0;
    }
    for(auto x: euler)
        fout << x << " ";
    return 0;
}