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

using namespace std;
ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");

int n,m,st=0,a[500010];

vector<int> v[100005];
stack<int> eul;


int main()
{   
    int i,j,x,y;
    in>>n>>m;
    for(int k=0;k<m;k++){
        in>>i>>j;
        v[i].push_back(j);
        v[j].push_back(i);
    }
    
    
    int imp=0;
    for(i=1;i<=n;i++)
        if(v[i].size()%2 != 0){
            imp=1;
            break;
        }
    
    if(imp)
        out<<-1;
    else{
        eul.push(1);
        while(!eul.empty()){
            x=eul.top();
            if(v[x].size()){
                y=v[x].back();
                v[x].pop_back();
                v[y].erase(find(v[y].begin(),v[y].end(),x));
                eul.push(y);
            }
            else{
                a[st++]=x;
                eul.pop();
            }
        }
    }
    for(int i=0;i<st-1;i++)
        out<<a[i]<<" ";

    in.close();
    out.close();
    return 0;
}