#include <fstream>
#include <vector>
using namespace std;
ofstream fout ("ciclueuler.out");
ifstream fin ("ciclueuler.in");
int n,m,i,a,b,grad[100005],st[100005],folosit[500005],ind[100005],nod,top,lung;
vector < pair < int , int > > w[100005];
pair < int , int > aux;
int main()
{
    fin>>n>>m;
    for( i = 1 ; i <= m ; i++ )
    {
        fin>>a>>b;
        w[ a ].push_back( { b , i } );
        w[ b ].push_back( { a , i } );
        grad[ a ]++;
        grad[ b ]++;
    }
    for( i = 1 ; i <= n ; i++ )
    {
        if( grad[ i ] == 0 || grad[ i ] % 2 )
        {
            fout<<-1;
            return 0;
        }
    }
    st[ 1 ] = 1;
    top = 1;
    while( top > 0 )
    {
        nod = st[ top ];
        lung = w[ nod ].size();
        while( ind[ nod ] < lung )
        {
            aux = w[ nod ][ ind[ nod ] ];
            if( folosit[ aux.second ] == 0 )
            {
                folosit[ aux.second ] = 1;
                st[ ++top ] = aux.first;
                break;
            }
            ind[ nod ]++;
        }
        if( ind[ nod ] == lung )
        {
            if( top > 0 )
            {
                fout<<nod<<" ";
                top--;
            }
        }
    }
}