#include <fstream>
#include <vector>

using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

const int nmax= 100000;
const int mmax= 500000;

vector <int> v[nmax+1];
int s[mmax+1];

int main(  ) {
    int n, m;
    fin>>n>>m;
    for ( int i= 1; i<=m; ++i ) {
        int x, y;
        fin>>x>>y;
        v[x].push_back(y);
        v[y].push_back(x);
    }

    for ( int i= 1; i<=n; ++i ) {
        if ( (int)v[i].size()%2==1 ) {
            fout<<"-1\n";
            return 0;
        }
    }

    int c= 1, l= 1;
    s[l]= 1;
    while ( l>0 ) {
        int x= s[l];
        if ( (int)v[x].size()>0 ) {
            int y= v[x][0];
            for ( int i= 0; i<(int)v[y].size(); ++i ) {
                if ( x==v[y][i] ) {
                    v[y][i]= v[y].back();
                    v[y].pop_back();
                    i= (int)v[y].size();
                }
            }

            ++l;
            s[l]= y;
            v[x][0]= v[x].back();
            v[x].pop_back();
        } else {
            while ( l>0 && v[s[l]].empty() ) {
                if ( c<=m ) {
                    fout<<s[l]<<" ";
                }
                --l;
                ++c;
            }
        }
    }
    fout<<"\n";

    return 0;
}