UVa 10219 - Find the ways ! Solution

#include <iostream>
#include <cmath>
using namespace std;
int main(){
    long long int a,b;
    while(cin>>a>>b){
        long double sum=0;
        for(long long int i=a;i>a-b;i--)
            sum+=log10((long double)i);
        for(long long int i=b;i>1;i--)
            sum-=log10((long double)i);
        cout<<(long long int)(floor(sum))+1<<endl;
    }
}