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

const int MAXN =  1e5 + 15;
const int INF = 1e8;

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

int n, m;
bool seen[5 * MAXN];
vector <pair <int, int>> g[MAXN];

void dfs(int node){

    while(g[node].size()){
        int y = g[node].back().first;
        int i = g[node].back().second;
        g[node].pop_back();

        if(!seen[i]){
            seen[i] = 1;

            dfs(y);
        }
    }
   if(m) fout << node << ' ' , m--;
}


int main(){

    fin >> n >> m;
    for(int i = 1; i <= m; ++i){
        int x, y; fin >> x >> y;
        g[x].push_back({y, i});
        g[y].push_back({x, i});
    }
    for(int i = 1; i <= n; ++i){
        if(g[i].size() % 2){
            fout << "-1";
            return 0;
        }
    }
    dfs(1);
    return 0;
}