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

#define nrmax 100001
using namespace std;

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

stack < int > st;
stack < int > sol;
bool used[nrmax];
int grad[nrmax];
vector < int > G[nrmax];
int n , m , x ,y , ok;

void dfs ( int i )
{
    used[i] = 1;
    for ( vector < int > ::iterator j = G[i].begin(); j != G[i].end() ; j++ )
    {
        if ( !used[ (*j) ])
            dfs( (*j) );
    }
}

void ciclu_eulerian(int i)
{
    st.push(i);
    while ( !st.empty() )
    {
        int nod = st.top();
        if ( G[nod].size() )
        {
            int vecin = G[nod][0];
            G[nod].erase(G[nod].begin());
            G[vecin].erase( find(G[vecin].begin(), G[vecin].end() , nod)) ;
            st.push(vecin);
        }
        else
        {
            st.pop();
            sol.push(nod);
        }
    }
}


int main()
{
    f >> n >> m ;
    for ( ; m-- ; )
    {
        f >> x >> y;
        G[x].push_back(y);
        G[y].push_back(x);
        grad[x]++;
        grad[y]++;
    }
    dfs(1);
    for ( int i = 1; i <= n ; i++ )
    {
        if ( !used[i] or grad[i]%2==1 )
        {
            g << -1;
            return 0;
        }
    }
    ciclu_eulerian(1);
    while( !sol.empty() )
    {
        int nod = sol.top();
        sol.pop();
        if ( !sol.empty() )
        g << nod << " " ;
    }
    return 0;
}