#include <iostream>
#include<fstream>
#include<stack>
#include<vector>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

const int NMAX = 100000;
int N, Mi;
vector<int> G[NMAX + 1], L ;
vector<pair<int, int>>M;
vector<bool>elim;
stack<int>S;
int Dim[NMAX+1];
void euler()
{
    S.push(1);
    while(!S.empty())
    {
        int v = S.top();
        if(G[v].size() > 0)
        {
            int x = G[v].back();
            G[v].pop_back();
            if(!elim[x])
            {
                elim[x] = 1;
                int p = M[x].second;
                if(p == v)
                    p = M[x].first;
                S.push(p);
            }
        }
        else
        {
            L.push_back(v);
            S.pop();
        }
    }
}

int main()
{
    int x, y;
    f >> N >> Mi;
    for(int i = 1; i <= Mi; i++)
    {
        f >> x >> y;
        M.push_back({x, y});
        elim.push_back(0);
        G[x].push_back(M.size() - 1);
        G[y].push_back(M.size() - 1);
        Dim[x]++;Dim[y]++;
    }
    int ok = 0;
    for(int i = 1; i <= N; i++)
        if(Dim[i] % 2)
        {
            g << -1;
            ok = 1;
            break;
        }
    if(!ok)
    {
        euler();
        int lung = L.size();
        for(int i = 0; i < lung - 1; i++)
            g << L[i] << ' ';
    }
    return 0;
}