#include <iostream>
#include <vector>
#include <stack>
#include <algorithm>
#define NMAX 100005
#include <fstream>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
int n,m,i,gr[NMAX],x,y;
vector <int> v[NMAX],ans;
stack <int> st;
void euler(int node)
{
    st.push(node);
    while(!st.empty())
    {
        int curr=st.top();
        if(v[curr].size())
        {
            int next=v[curr].back();
            v[curr].pop_back();
            v[next].erase(find(v[next].begin(),v[next].end(),curr));
            st.push(next);
        }
        else
        {
            st.pop();
            ans.push_back(curr);
        }
    }
}
int main()
{
    f>>n>>m;
    for(i=1;i<=m;i++)
    {
        f>>x>>y;
        v[x].push_back(y);
        v[y].push_back(x);
        gr[x]++;
        gr[y]++;
    }
    for(i=1;i<=n;i++)
    {
        if(gr[i]%2==1 || gr[i]==0)
        {
            g<<-1;
            return 0;
        }
    }
    euler(1);
    for(i=0;i<=ans.size()-1;i++)
    {
        g<<ans[i]<<" ";
    }
    return 0;
}