#include <iostream>
#include <fstream>
#include <stack>
#include <vector>
using namespace std;
ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");
int n,m,grad[100005],i,x,y,lung, ll[100005],z;
vector< pair <int,int> > a[100005];
bool v[500005];
stack<int> st;

void citire(){
    in>>n>>m;
    for(i=1;i<=m;++i){
        in>>x>>y;
        a[x].push_back({y, i});
        a[y].push_back({x, i});
        grad[x]++;
        grad[y]++;
    }
}

int main()
{
    citire();
    for(i=1;i<=n;i++){
        if(grad[i]%2 || !grad[i]){
            out<<-1;
            return 0;
        }
    }
    st.push(1);
    while(!st.empty()){
        x=st.top();
        lung=a[x].size();
        while(ll[x]<lung){
            y=a[x][ll[x]].first;
            z=a[x][ll[x]].second;
            if(!v[z]){
                v[z]=1;
                st.push(y);
                break;
            }
            ll[x]++;
        }
        if(ll[x] == lung)
        {
            out<<x<<" ";
            st.pop();
        }

    }
    return 0;
}