#include <fstream>
#include <vector>
#include <bitset>
#include <iostream>
using namespace std;

const int N = 1e5;
const int M = 5e5;

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

struct muchie{
    int x, y;
};

muchie e[M];
bitset<M> sterse;
int n, m, prim[N+1];

vector<int> a[N+1];
vector<int> ce;

bool toate_gradele_pare(){
    for(int i=1; i <= n; i++){
        if(a[i].size() % 2 != 0)
            return false;
    }
    return true;
}

int celalalt_vf(muchie e, int x){
    return (e.x + e.y - x);
}

void euler(int x){
    while(prim[x] < (int)a[x].size()){
        int i_e_c = a[x][prim[x]++];
        muchie e_c = e[i_e_c];
        int y = celalalt_vf(e_c, x);
        if (!sterse[i_e_c]){
            sterse[i_e_c] = 1;
            euler(y);
        }
    }
    ce.push_back(x);
}

int main(){
    in >> n >> m;
    for(int i = 0; i < m; i++){
        in >> e[i].x >> e[i].y;
        a[e[i].x].push_back(i);
        a[e[i].y].push_back(i);
    }

    if(!toate_gradele_pare()){
        out << "-1";
        return 0;
    }
    euler(1);
    if((int)ce.size() != m + 1){
        out << "-1";
        return 0;
    }
    for(int i = 0; i < (int)ce.size() - 1; i++)
        out << ce[i] << " ";
}