#include <fstream>
#include <vector>
#include <bits/stdc++.h>
#define NN 100001
#define MM 500001
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
int n,m,i,x,y,l[NN];
bool viz[MM];
vector <int>  G[NN],sol;
void Euler(int u) {
    vector<int> stk;
    stk.push_back(u);
    int v;
    viz[u]=1;
    while(!stk.empty())
    {
        u = stk.back();
        if(!G[u].empty())
        {
            v = G[u].back();
            G[u].pop_back();
            G[v].erase( find(G[v].begin(), G[v].end(), u) );
            stk.push_back(v);
            viz[v]=1;
        }
        else
        {
            sol.push_back(u);
            stk.pop_back();
        }
    }
}
int main()
{
    f>>n>>m;
    for(i=1;i<=m;i++)
    {
        f>>x>>y;
        G[x].push_back(y);
        G[y].push_back(x);
        l[x]++;
        l[y]++;
    }
    for(i=1;i<=n;i++)
        if(l[i]%2) {g<<-1; return 0;}
    Euler(1);
    for(i=1;i<=m;i++) if(viz[i]==0) {g<<-1; return 0;}
    for(i=0;i<sol.size()-1;i++) g<<sol[i]<<' ';
    return 0;
}