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

using namespace std;

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

const int maxn = 1e5+5, maxm = 5e5+5;

struct xy {
    int x, y;
};

int n, m;
vector <xy> v[maxn];
vector <int> ans;
int gr[maxn];
stack <int> st;
bool done[maxm];

void euler() {
    int x;
    st.push(1);
    while(!st.empty()) {
        x = st.top();
        if(gr[x] != 0) {
            if(done[v[x][gr[x]-1].y] == false) {
                done[v[x][gr[x]-1].y] = true;
                st.push(v[x][gr[x]-1].x);
            }
            gr[x] --;
        } else {
            st.pop();
            ans.push_back(x);
        }
    }
    for(auto u = ans.begin(); u != ans.end() - 1; u ++) {
        g << *u << ' ';
    }
    g << '\n';
}

int main() {
    int i, x, y;
    f >> n >> m;
    for(i = 1; i <= m; i ++) {
        f >> x >> y;
        v[x].push_back({y, i});
        v[y].push_back({x, i});
        gr[x] ++;
        gr[y] ++;
    }

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

    euler();

    return 0;
}