#include <fstream>
#include <vector>
#define Nmax 500010
 
using namespace std;

ifstream f("ciclueuler.in");
ofstream gout("ciclueuler.out");
	
vector<int> v[Nmax];
vector<int> g[Nmax];
int gr[Nmax];
int viz[Nmax];
int n,m;
int nr1=0;
 
void dfs(int nod)
{
    int i;
    for (i=0;i<v[nod].size();++i)
         if (!viz[v[nod][i]])
         {
             viz[v[nod][i]]=1;
             dfs(g[nod][i]);
         }
    gout<<nod<<" ";
}   
 
void citire()
{


    int i,x,y;
     
    f>>n>>m;
    for (i=1;i<=m;++i)
    {
        f>>x>>y;
        gr[x]++;
        gr[y]++;
        g[x].push_back(y);
        g[y].push_back(x);
        v[x].push_back(i);
        v[y].push_back(i);
        if (x==1 && y==2) 
			nr1++; 
	}
}
 
int main()
{
    int i;
    citire();
     
    for (i=1;i<=n;++i)
         if (gr[i]%2==1)
         {
             gout<<"-1";
             return 0;
         }
             
     dfs(1);
     
    return 0;
}