#include <iostream>
#include <fstream>
#include <unordered_map>
#include <vector>
#include <stack>

using namespace std;

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

vector<int> vec[100003];
int intr[100003];
stack<int> rez;
bool rem[500003];
pair<int, int> edg[500003];

void eul(int nod) {

    int crr;
    pair<int, int> T;
    stack<int> S;
    S.push(nod);

    while(!S.empty()) {

        nod = S.top();

        if(vec[nod].empty()) {
            rez.push(nod);
            S.pop();
            continue;
        }

        T = edg[vec[nod].back()];

        if(rem[vec[nod].back()]) {
            vec[nod].pop_back();
            continue;
        }

        rem[vec[nod].back()] = true;

        if(T.first == nod)
            crr = T.second;
        else
            crr = T.first;

        S.push(crr);

    }

}

int main() {

    int n,m;
    in >> n >> m;
    int x,y;

    for(int i = 1; i <= m; i++) {

        in >> x >> y;

        vec[x].push_back(i);
        vec[y].push_back(i);
        edg[i] = {x, y};
        intr[x]++;
        intr[y]++;

    }

    for(int i = 1; i <= n; i++) {
        if(intr[i]%2 == 1) {
            out << -1;
            return 0;
        }
    }

    eul(1);

    while(!rez.empty()) {
        out << rez.top() << " ";
        rez.pop();
    }

    return 0;
}