#include <fstream>
#include <vector>

using namespace std;

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

#define MaxN 200001

int n, m;
vector<int> G[MaxN], sol;
pair<int,int> E[MaxN];
bool viz[MaxN], ok = true;

inline void Df(int);

int main() {

    fin >> n >> m;

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

    for ( int i = 1; i <= n; ++i )
        if ( G[i].size() % 2 )
            ok = false;

    if ( ok ) {

    Df(1);

    for ( int i = 0; i < sol.size() - 1; ++i )
        fout << sol[i] << ' ';
    }
    else
        fout << "-1/n";


    fin.close();
    fout.close();
    return 0;
}

inline void Df(int i) {

    for ( const auto y : G[i] )
        if ( !viz[y] ) {
            viz[y] = true;
            if ( E[y].first == i )
                Df(E[y].second);
            else
                Df(E[y].first);
        }
    sol.push_back(i);
}