#include<fstream>
#include<vector>
#include<stack>

using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int const N = 5e5 + 3;
int n , m;
int st[N] , dr[N] , viz[N];
vector<int> v[N];
stack<int> stk;
int main(){
    fin >> n >> m;
    for(int i = 1 ; i <= m ; ++ i){
        fin >> st[i] >> dr[i];
        v[st[i]].push_back(i);
        v[dr[i]].push_back(i);
    }
    for(int i = 1 ; i <= n ; ++ i){
        if(v[i].size() & 1){
            fout << "-1\n";
            return 0;
        }
    }
    stk.push(1);
    while(!stk.empty()){
        int x = stk.top();
        if(v[x].empty()){
            stk.pop();
            if(!stk.empty())
                fout << x << ' ';
        }else{
            int e = v[x].back();
            v[x].pop_back();
            if(viz[e])
                continue;
            viz[e] = 1;
            int y = st[e] ^ dr[e] ^ x;
            stk.push(y);
        }
    }
    return 0;
}