#include <iostream>
#include <stdio.h>
#include <vector>
#include <stack>
#include <algorithm>
#define NMax 100005
using namespace std;
vector<int> Graf[NMax],Sol;
int N,M,x,y,z,rang[NMax];
stack<int> Stiva;
bool mark[NMax];

void Read()
{
    scanf("%d%d",&N,&M);
    for(int i=1;i<=M;i++)
    {
        scanf("%d%d",&x,&y);
        Graf[x].push_back(y);
        Graf[y].push_back(x);
        rang[x]++;
        rang[y]++;
    }
}

void Euler()
{
    Stiva.push(1);
    while(Stiva.empty()==false)
    {
        int x=Stiva.top();
        if(Graf[x].size()==0)
        {
            Sol.push_back(x);
            Stiva.pop();
        }
        else
        {
            int y=Graf[x][Graf[x].size()-1];
            Graf[x].pop_back();
            Stiva.push(y);
            Graf[y].erase(find(Graf[y].begin(),Graf[y].end(),x));
        }
    }
}

void Write()
{
    Sol.pop_back();
    for(int i=0;i<Sol.size();i++)
        printf("%d ",Sol[i]);
}

int main()
{
   freopen("ciclueuler.in","r",stdin);
   freopen("ciclueuler.out","w",stdout);
   Read();

   for(int i=1;i<=N;i++)
       if(rang[i]%2==1)
       {
           printf("-1");
           return 0;
       }

   Euler();
   Write();
}