#include <fstream>
#include <list>
#include <algorithm>
#define NMAX 100010

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int n,m,i,j,vf,x,y,st[NMAX*5];
list<int> l[NMAX];

int main()
{
    f>>n>>m;
    for(i=1; i<=m; ++i) f>>x>>y,l[x].push_back(y),l[y].push_back(x);
    for(i=1; i<=n; ++i)
        if(l[i].size()%2)
        {
            g<<-1<<'\n';
            return 0;
        }
    vf=1,st[vf]=1;
    while(vf>0)
    {
        x=st[vf];
        while(!l[x].empty()) y=l[x].front(),l[x].pop_front(),l[y].erase(find(l[y].begin(),l[y].end(),x)),vf++,st[vf]=y,x=y;
        g<<st[vf--]<<' ';
    }
    return 0;
}