#include <bits/stdc++.h>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
#define MAXN 100001
#define pb push_back
#define it vector<int>::iterator
vector <int> G[MAXN];
int N,M,x,y,i,j;
int grad[MAXN];
bool used[MAXN];
stack<int>st;
vector<int>sol;
void dfs(int i)
{
    used[i] = 1;
    for ( vector<int>::iterator j=G[i].begin();j!=G[i].end();j++)
    {
        if(!used[(*j)]) dfs(*j);
    }
}
void euler(int i)
{
    st.push(i);
    while(!st.empty())
    {
        int n = st.top();
        if(G[n].size())
        {
            int vecin = G[n].back();
            G[n].pop_back();
            st.push(vecin);
            G[vecin].erase(find(G[vecin].begin(),G[vecin].end(),n));
        }
        else
        {
            sol.push_back(n);
            st.pop();
        }
    }
    for(int i=0;i<sol.size()-1;i++)
        g<<sol[i]<<" ";
}

int main()
{
    f >> N >> M;
    for ( ; M-- ; )
    {
        f >> x >> y;
        G[x].pb(y);
        G[y].pb(x);
        grad[x]++;
        grad[y]++;
    }
    dfs(1);
    for(i=1;i<=N;i++)
        if(!used[i] or grad[i]%2)
        {
            g<<-1;
            return 0;
        }
    euler(1);

    return 0;
}