#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
#define LE 500666
int result[LE],grad[LE];
int viz[LE];
#include <vector>
vector<pair<int,int> > H[LE];
#define x first
#define y second
int K;

void dfs(int nod) {
    int N=H[nod].size();
    int i;

    for(i=0; i<N; ++i){
        if (viz[H[nod][i].y]==0) {
            viz[H[nod][i].y]=1;
            dfs(H[nod][i].x);
        }
    }
    result[++K]=nod;
}
#define mp make_pair
#define pb push_back
int main() {
    int n,m,x,y,i;

    f>>n>>m;
    for(i=1; i<=m; ++i) {
        f>>x>>y;
        H[x].pb(mp(y,i));
        H[y].pb(mp(x,i));
        grad[x]++;
        grad[y]++;
    }

    for(i=1; i<=n; ++i) if (grad[i]%2) {
            g<<-1;
            return 0 ;
        }
    dfs(1);

    for(i=1; i<K; ++i)
        g<<result[i]<<" ";

    f.close();
    g.close();
    return 0;
}