#include <fstream>
#include <vector>
#include <stack>
#include <algorithm>
using namespace std;
ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");

#define MAXN 100005

vector<int> graf[MAXN];
stack<int> st;
int n,m,i,j,x,y,nod;
bool euler = true;

int main()
{
    cin>>n>>m;
    for(i=1; i<=m; i++)
    {
        cin>>x>>y;
        graf[x].push_back(y);
        graf[y].push_back(x);
    }
    for(i=1; i<=n; i++)
        if(!graf[i].size() || graf[i].size() % 2 ==1)
            euler=false;

    if(!euler)
    {
        cout<<-1;
        return 0;
    }

    st.push(1);
    while(!st.empty())
    {
        nod=st.top();
        if(!graf[nod].size())
        {
            st.pop();
            if( !st.empty() )
                cout<<nod<<" ";
        }
        else
        {
            x=graf[nod].back(); graf[nod].pop_back();
            graf[x].erase(  find(graf[x].begin(), graf[x].end(), nod) );
            st.push(x);
        }
    }
}