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

const int NMAX = 100001;
const int MMAX = 500001;

int to[MMAX];
int from[MMAX];

bool used[MMAX];
int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(NULL);

    int n, m;
    std::cin >> n >> m;
    std::vector<std::vector<int>>g;
    g.resize(n + 1);
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        std::cin >> x >> y;
        g[x].push_back(i);
        g[y].push_back(i);
        from[i] = x;
        to[i] = y;
    }

    for(int i = 1; i <= n; ++i)
    {
        if(g[i].size() % 2 == 1){
            std::cout << -1 << '\n';
            return 0;
        }
    }

    std::stack<int>st;
    st.push(1);
    //incepem din nodul 1 accesam fiecare muchie

    std::vector<int>ans;
    while(!st.empty())
    {
        int node = st.top();

        if(!g[node].empty())
        {
            int muchie = g[node].back();
            g[node].pop_back();

            if(!used[muchie])
            {
                used[muchie] = true;
                if(node == from[muchie])
                {
                    st.push(to[muchie]);
                }
                else st.push(from[muchie]);
            }
        }
        else {
            st.pop();
            ans.push_back(node);
        }

    }

    for(size_t i = 0; i < ans.size() - 1; ++i)
        std::cout << ans[i] << ' ';

    return 0;
}