#include <iostream>
#include <stdio.h>
#include <vector>
#include <stack>
#include <algorithm>
#define NMax 100005
using namespace std;
vector<int> Graf[NMax],Sol;
stack<int> Stiva;
int N,M,x,y,rang[NMax];
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 nodx=Stiva.top();
        if(Graf[nodx].size()==0)
        {
            Sol.push_back(nodx);
            Stiva.pop();
        }
        else
        {
            int nody=Graf[nodx][Graf[nodx].size()-1];
            Graf[nodx].pop_back();
            Graf[nody].erase(find(Graf[nody].begin(),Graf[nody].end(),nodx));
            Stiva.push(nody);
        }
    }
}

void Write()
{
    Sol.pop_back();
    for(vector<int>::iterator it=Sol.begin();it!=Sol.end();it++)
        printf("%d ",*it);
}

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)
        {
            return 0;
            printf("-1");
        }

    Euler();
    Write();
}