#include <bits/stdc++.h>
#define NMAX 100100

using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
vector < int > v[NMAX];
int n,m,conex;
int fr[NMAX],gr[NMAX];
bool ok=true;
int sol[NMAX],p;
void dfs(int i)
{
    fr[i]=1;
    for( auto x : v[i])
        if(!fr[x])dfs(x);
}
void euler(int i)
{
    vector<int>::iterator it= v[i].begin();
    while(it!=v[i].end())
    {
        int val=*it;
        it=v[i].erase(it);
        v[val].erase(find(v[val].begin(),v[val].end(),i));
        euler(val);
    }

    sol[++p]=i;
}
int main()
{
    fin>>n>>m;
    for(int i=1;i<=m;++i)
    {
        int x,y;
        fin>>x>>y;
        ++gr[x];
        ++gr[y];

       v[x].push_back(y);
       v[y].push_back(x);


    }
    for(int i=1;i<=n&&ok;++i)
    {
        if(gr[i]%2==1){ok=false;continue;}

    }
    if(!ok)fout<<-1;
    else
    {
        euler(1);
        for(int i=1;i<=p;++i)fout<<sol[i]<<" ";
    }
    return 0;
}