#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

struct _muchie{
    int a, b;
} muchie[500001]={0};

vector<int> v[100001],stack;
bool viz[500001];
int sol[500001], lg, w;

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

int main()
{
    int i, n, m, nod, w, a, b;
    f>>n>>m;
    for(i=1; i<=m; i++)
        {f>>a>>b;
        v[a].push_back(i);
        v[b].push_back(i);
        muchie[i].a = a;
        muchie[i].b = b;
    }

    for(i=1; i<=n; i++)
        if(v[i].size() % 2){

            g<<"-1";
            return 0;
        }

    stack.push_back(1);
    while(!stack.empty())
        {nod = stack.back();
        if(!v[nod].empty())
        {w=v[nod].back();
        v[nod].pop_back();
        if(!viz[w])
        {viz[w] = true;
        if(muchie[w].a == nod)stack.push_back(muchie[w].b);
                         else stack.push_back(muchie[w].a);
            }
        }
        else{
            sol[++lg] = nod;
            stack.pop_back();
        }
    }

    for(i=1; i<lg; i++)
        g<<sol[i]<<" ";

}