#include<cstdio>
#include<algorithm>
#include<stack>
#include<vector>
#include<deque>
using namespace std;
int n,i,j,k,grad[100005],x,y,m;
stack<int>s;
vector<int>v[100005];
deque<int>c;
bool viz[100005];

void df(int x)
{
    viz[x]=true;
    for (int j=0;j<v[x].size();j++)
        if (!viz[v[x][j]])
            df(v[x][j]);
}
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),v[x].push_back(y),v[y].push_back(x),grad[x]++,grad[y]++;
    df(1);
    for (i=1;i<=n;i++)
        if (grad[i]%2==1 || !viz[i])
        {
            printf("-1\n");
            return 0;
        }
    s.push(1);
    while (!s.empty())
    {
        x=s.top();
        if (!v[x].size()) printf("%d ",x),s.pop();else
            {
              s.push(v[x].back());
              y=v[x].back();
              v[y].erase(find(v[y].begin(),v[y].end(),x));
              v[x].pop_back();
            }
    }
    return 0;
}