#include <fstream>
#include <vector>

using namespace std;

int n, m;
vector<int> L[100005];
pair<int, int> edge[500005];
int viz[500005];

int main()
{
    ifstream f("ciclueuler.in");
    ofstream g("ciclueuler.out");

    f >> n >> m;
    int x, y;
    for(int i = 1; i <= m; i ++) {
        f >> x >> y;
        edge[i].first = x;
        edge[i].second = y;
        L[x].push_back(i);
        L[y].push_back(i);
    }

    for(int i = 1; i <= n; i ++) {
        if(L[i].size() % 2 != 0) {
            g << "-1\n";
            return 0;
        }
    }

    vector<int> stk, ans;
    stk.push_back(1);
    while(!stk.empty()) {
        int x = stk.back();
        if(!L[x].empty()) {
            int e = L[x].back();
            L[x].pop_back();
            if(!viz[e]) {
                viz[e] = true;
                if(edge[e].first == x)
                    stk.push_back(edge[e].second);
                else stk.push_back(edge[e].first);
            }
        }
        else {
            stk.pop_back();
            ans.push_back(x);
        }
    }

    for(int i = 0; i < ans.size(); i ++)
        g << ans[i] << " ";
    g << "\n";
    return 0;
}