#include <vector>
#include <set>
#include <algorithm>
#include <cctype>
#include <cstdlib>
#include <cmath>
#include <stack>
#include <queue>
#include <cstring>
#include <string>
#include <cstdio>
#include <climits>
#include <list>
#define PII pair < int , int >
#define MP make_pair
#define PB push_back
#define F first
#define S second
#define LL long long
#define NMAX 20
using namespace std;
vector <int> G[100001];
list <int> Q;
int m, n, i, x, y;
void euler (int x)
{
    vector <int> :: iterator it;
    Q.push_front(x);
    while (!Q.empty())
    {
        x=Q.front();
        if (G[x].empty())
        {
            Q.pop_front();
            if (!Q.empty()) printf("%d ",x);
        }
        else
        {
            int y=G[x].back();
            Q.push_front(y);
            G[x].pop_back();
            for (it=G[y].begin(); it!=G[y].end(); it++)
            {
                if (*it==x)
                {
                    G[y].erase(it);
                    break;
                }
            }
        }
    }
}
int main()
{

    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d%d",&n,&m);
    for (i=1; i<=m; i++)
    {
        scanf("%d%d",&x,&y);
        G[x].PB(y);
        G[y].PB(x);
    }
    for (i=1; i<=n; i++)
    {
        if (G[i].size()%2!=0)
        {
            printf("-1");
            return 0;
        }
    }
    euler(1);

    return 0;
}