#include <iostream>
#include <fstream>
#include <vector>
#include <stack>

using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

const int Nmax = 100005;
bool sw = 1;
int n, m, Grad[Nmax], Use[Nmax];
vector <int> G[Nmax], Sol;
stack <int> S;

void DFS(int Nod)
{
    Use[Nod] = 1;
    for(int i = 0; i < (int)G[Nod].size(); i ++)
    {
        int Vecin = G[Nod][i];
        if(!Use[Vecin]) DFS(Vecin);
    }
}

void Erase(int nod1, int nod2)
{
    G[nod1].erase(G[nod1].begin());
    for(int i = 0; i < (int)G[nod2].size(); i++)
        if(G[nod2][i] == nod1)
        {
            G[nod2].erase(G[nod2].begin() + i);
            break;
        }
}

void Ciclu(int nod)
{
    while(G[nod].size())
    {
        S.push(nod);
        int vecin = G[nod][0];
        Erase(nod, vecin);
        nod = vecin;
    }
}

void Solve()
{
    DFS(1);
    for(int i = 1; i <= n; i++)
        if(Grad[i]%2 || !Use[i]) sw = 0;
    if(!sw) return;
    int nod = 1;
    do
    {
        Ciclu(nod);
        nod = S.top(); S.pop();
        Sol.push_back(nod);
    }while(!S.empty());
}

void Print()
{
    if(sw == 0) g<<"-1";
    else for(int i = 0; i < (int)Sol.size(); i++) g<<Sol[i]<<' ' ;
    g<<'\n';
}

void Read()
{
    f>>n>>m;
    for(int i = 1; i <= m; i++)
    {
        int x,y;
        f>>x>>y;
        G[x].push_back(y);
        G[y].push_back(x);
        Grad[x]++;
        Grad[y]++;
    }
}

int main()
{
    Read();
    Solve();
    Print();
    return 0;
}