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

using namespace std;

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

const int NMAX = 1e5;
const int MMAX = 5e5;

int N, M;
vector <pair<int,int>> g[NMAX + 2];
int deg[NMAX + 2];

bool d[MMAX + 2];

int main()
{
    cin >> N >> M;

    for(int i = 1; i <= M; i++)
    {
        int x, y;
        cin >> x >> y;
        g[x].push_back({y, i});
        g[y].push_back({x, i});

        deg[x]++, deg[y]++;
    }

    for(int i = 1; i <= N; i++)
        if(deg[i] % 2 == 1)
        {
            cout << -1;
            return 0;
        }

    vector <int> res;

    stack <int> st;
    st.push(1);

    while(!st.empty())
    {
        int node = st.top();

        while(!g[node].empty() && d[g[node].back().second])
            g[node].pop_back();

        if(!g[node].empty())
        {
            st.push(g[node].back().first);
            d[g[node].back().second] = true;
            g[node].pop_back();
        }
        else
            res.push_back(node), st.pop();
    }


    for(int i = 1; i < (int)res.size(); i++)
        cout << res[i] << ' ';

    return 0;
}