#include <fstream>
#include <cstring>
#include <vector>
std::ifstream cin("ciclueuler.in");
std::ofstream cout("ciclueuler.out");
using namespace std;
#define maxn 500505
vector<int> G[maxn];
bool used_edge[maxn];
int from[maxn],to[maxn], N,M;

void citire(){
    int x,y;
    cin>>N>>M;
    for(int i=1;i<=M;i++){
        cin>>x>>y;
        G[x].push_back(i);
        G[y].push_back(i);
        from[i]=x;
        to[i]=y;
    }
}


int main()
{
    int node;
    citire();
    for(int i=1;i<=N;i++)
        if(G[i].size()&1){
            cout<<"-1\n";
            return 0;
    }
    vector<int> ans,stk;
    stk.push_back(1);
    while(!stk.empty()){
        node=stk.back();
        if(!G[node].empty()){
            int e=G[node].back();
            G[node].pop_back();
            if(!used_edge[e]){
                used_edge[e]=true;
                int to=from[e] ^ ::to[e] ^ node;//:: operator is for accesing an global variable when there is a local variable with the same name
                stk.push_back(to);
            }
        }else{
            stk.pop_back();
            ans.push_back(node);
        }
    }
     for(vector<int>::iterator it=ans.begin();it!=ans.end()-1;it++)
        cout<<*it<<' ';

    return 0;
}
*/