Combination

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;

#define rapid_io() ios::sync_with_stdio(false);cin.tie(0);
#define endl '\n'
#define pb push_back
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()

int main()
{
    rapid_io();
    int n,m;
    while(cin>>n>>m)
    {
        if(n==0 && m==0)
            return 0;
        int arr1[n+1],arr2[m+1];
        for(int i=n-m+1;i<=n;i++)
        {
            arr1[i]=i;
        }
        for(int i=1;i<=m;i++)
        {
           arr2[i]=i;
        }
        for(int i=1;i<=m;i++)
        {
            for(int j=n-m+1;j<=n;j++)
            {
                if(arr1[j]%arr2[i]==0)
                {
                    arr1[j]=arr1[j]/arr2[i];
                    arr2[i]=1;
                }
            }
        }
        ll ans=1,lob=1,hor=1;

        for(int i=n-m+1;i<=n;i++)
        {
            lob*=arr1[i];
        }
        for(int i=1;i<=m;i++)
        {
            hor*=arr2[i];
        }
        ans=lob/hor;

        cout<<n<<" things taken "<<m<<" at a time is "<<ans<<" exactly."<<endl;
    }



    return 0;
}