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

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

vector<pair<int, int> > g[100005];
int n, m;
bool used[500005];
vector<int> ciclu;

void citire() {
    fin >> n >> m;
    while(m--) {
        int x, y;
        fin >> x >> y;
        g[x].push_back({y, m});
        g[y].push_back({x, m});
    }
}

void dfs(int x) {
    while(g[x].size()) {
        pair<int, int> next = g[x].back();
        g[x].pop_back();

        if(!used[next.second]) {
            used[next.second] = true;
            dfs(next.first);
        }
    }
    ciclu.push_back(x);
}

void solve() {
    for(int i = 1; i <= n; i++)
        if(g[i].size()%2) {
            fout << -1;
            return;
        }

    dfs(1);
}

void afis() {
    ciclu.pop_back();
    for(auto x: ciclu)
        fout << x <<  ' ';
}

int main() {
    citire();
    solve();
    afis();
}