#include <cstdio>
#include <vector>
#include <stack>

using namespace std;

stack<int> st;
vector<int> g[100002];
bool vis[100002];

void dfs(int node)
{
    vis[node] = true;
    for (unsigned i = 0; i < g[node].size(); i++)
        if (!vis[g[node][i]])
            dfs(g[node][i]);
}

void deleteEdge(int v, int w)
{
    for (vector<int>::iterator it = g[v].begin(); it != g[v].end(); it++)
        if (*it == w)
        {
            g[v].erase(it);
            return;
        }
}

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);

    int n, m;
    scanf("%d%d", &n, &m);
    for (int i = 1, x, y; i <= m; i++)
    {
        scanf("%d%d", &x, &y);
        g[x].push_back(y);
        g[y].push_back(x);
    }

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

    st.push(1);
    while (!st.empty())
    {
        int v = st.top();
        if (g[v].size() == 0)
        {
            st.pop();
            if (!st.empty())
                printf("%d ", v);
        }
        else
        {
            int w = g[v].back();
            g[v].pop_back();
            deleteEdge(w, v);
            st.push(w);
        }
    }
    printf("\n");

    return 0;
}