#include <algorithm>
#include <fstream>
#include <stack>
#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];
stack <int> s;
int sol[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;
    s.push(1);
    while ( !s.empty() ) {
        int x= s.top();
        if ( (int)v[x].size()>0 ) {
            int y= v[x].back();
            v[x].pop_back();
            s.push(y);
            v[y].erase( find( v[y].begin(), v[y].end(), x ) );
        } else {
            sol[++c]= x;
            s.pop();
        }
    }

    for ( int i= 0; i<c; ++i ) {
        fout<<sol[i]<<" ";
    }
    fout<<"\n";

    return 0;
}