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

#define NMAX 100001
#define MMAX 500005

using namespace std;

int n, m, x, y, ok = 1;
vector<int> v[NMAX];
stack<int> S;

void euler()
{
    S.push(1);
    while(!S.empty())
    {
        int nod = S.top();
        while(!v[nod].empty())
        {
            int w = v[nod].back();
            v[nod].pop_back();
            int pos = -1;
            for(int i = 0; i < v[w].size(); i++)
                if(v[w][i] == nod)
                    pos = i;
            if(pos != -1)
                v[w].erase(v[w].begin() + pos);
            S.push(w);
        }
        S.pop();
        printf("%d ", nod);
    }
}

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);
        v[x].push_back(y);
        v[y].push_back(x);
    }
    for(int i = 1; i <= n; i++)
        if(v[i].size() % 2 == 1)
        {
            printf("-1");
            ok = 0;
            break;
        }
    if(ok)
        euler();
    return 0;
}