UVa 10219 - Find the ways !

#include<bits/stdc++.h>
#include<cmath>
#define ll long long

using namespace std;

int main()
{
  unsigned ll n,k;
  long double sum;
  
 while(cin>>n>>k)
 {
  sum=0;
  
  for( unsigned ll i=n-k+1; i<=n; i++)
  {
   sum+=log10((double)i);
  }
  
   for( unsigned ll j=1; j<=k; j++)
   {
    sum-=log10((double)j);
   }
   
   cout<<(ll)sum+1<<endl;
  } 
 return 0;
}