#include <iostream>
#include <vector>
#include <fstream>
using namespace std;
ifstream f("ciclueuler.in");
ofstream b("ciclueuler.out");
vector <int> g[100005];
vector <int> a;
void euler(int u)
{
    int v;
    unsigned int j;
   // cout<<u;
    while(g[u].size()!=0)
    {
        v=g[u].back();
        g[u].pop_back();
        for(j=0;j<g[v].size();j++)
        if(g[v][j]==u)
        {
            g[v][j]=g[v][g[v].size()-1];
            g[v].pop_back();
            break;
        }
        euler(v);
    }
        a.push_back(u);
}
int main()
{

    int n,m,x,y,ok=1;
    f>>n>>m;
    for(int i=1;i<=m;i++)
    {
        f>>x>>y;
        g[x].push_back(y);
        g[y].push_back(x);
    }
    for(int i=1;i<=n;i++)
        if(g[i].size()%2!=0)
        ok=0;
    if(ok==0)
        b<<ok-1;
    else
    {
        euler(1);
        for(int i=0;i<a.size();i++)
            b<<a[i]<<" ";
    }

}