#include <iostream>
#include <cstdio>
#include <vector>
#include <stack>
#include <bitset>

#define NMAX 100001
#define MMAX 500005

using namespace std;

int n, m, x, y, ok = 1;
vector<int> v[NMAX];
stack<int> S;
vector<pair<int, int> > M;
bitset<MMAX> viz;

void euler()
{
    S.push(1);
    while(!S.empty())
    {
        int nod = S.top();
        if(!v[nod].empty())
        {
            int mi = v[nod].back();
            v[nod].pop_back();
            if(!viz[mi])
            {
                int w = 0;
                if(nod == M[mi].first)
                    w = M[mi].second;
                else if(nod == M[mi].second)
                    w = M[mi].first;
                viz[mi] = 1;
                S.push(w);
            }
        } else {
            printf("%d ", nod);
            S.pop();
        }
    }
}

int main()
{
    freopen( "ciclueuler.in", "r",  stdin);
    freopen("ciclueuler.out", "w", stdout);
    scanf("%d %d\n", &n, &m);
    for(int i = 0; i < m; i++)
    {
        scanf("%d %d\n", &x, &y);
        M.push_back(make_pair(x, y));
        v[x].push_back(M.size() - 1);
        v[y].push_back(M.size() - 1);
    }
    for(int i = 1; i <= n; i++)
        if(v[i].size() % 2 == 1)
        {
            printf("-1");
            ok = 0;
            break;
        }
    if(ok)
        euler();
    return 0;
}