#include <bits/stdc++.h>

using namespace std;

int n, m;
vector<int> G[100005];
stack<int> st;
queue<int> q;
bool ok = 1;

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    int u, v;
    scanf("%d%d", &n, &m);
    for(int i = 0; i < m; i++)
    {
        scanf("%d%d", &u, &v);
        G[v].push_back(u);
        G[u].push_back(v);
    }
    for(int i = 1; i < n; i++) if(G[i].size() & 1 or !G[i].size()) { ok = 0; return 0 * printf("-1"); }
    printf("1");
    q.push(1);
    while(!q.empty())
    {
        u = q.front();
        q.pop();
        if(!ok) break;
        if(G[u].size()) st.push(u);
        int v;
        v = G[u].back();
        G[u].pop_back();
        G[v].erase(find(G[v].begin(), G[v].end(), u));
        if(G[v].size()) { q.push(v); continue; }
        if(!G[v].size())
        {
            while(!st.empty() and !G[v].size())
            {
                v = st.top();
                st.pop();
                printf(" %d", v);
            }
            if(!st.empty()) { q.push(v); continue; }
            else
            {
                for(int i = 0; i < n; i++) if(G[i].size()) { ok = 0; break; }
            }
        }
    }
    if(ok) fseek(stdout, -2, SEEK_END), printf("  ");
    else freopen("ciclueuler.out", "w", stdout), printf("-1");
    return 0;
}