#include <fstream>
#include <vector>
#include <stack>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
#define nmax 100005
#define mmax 500005
vector<int> v[nmax], sol;
int n, m, to[mmax], from[mmax], x, y;
bool u[mmax];
int main()
{
    f >> n >> m;
    for (int i = 0; i < m; ++i){
        f >> x >> y;
        v[x].push_back(i), v[y].push_back(i);
        from[i] = x;
        to[i] = y;
    }
    for (int i = 1; i <= n; ++i)
        if(v[i].size() & 1){ g << "-1\n"; return 0; }
    stack<int> q;
    q.push(1);
    while(!q.empty()){
        int nod = q.top();
        if(v[nod].size() == 0){
            q.pop();
            sol.push_back(nod);
        }
        else {
            int e = v[nod].back();
            v[nod].pop_back();
            if(!u[e]){
                u[e] = 1;
                int qnxt = from[e];
                if(nod == from[e])
                    qnxt = to[e];
                q.push(qnxt);
            }
        }
    }
    for (unsigned int i = 0; i < sol.size() - 1; ++i) g << sol[i] << " ";
    return 0;
}