Combinari(n,k) cu invers modular

#include <bits/stdc++.h>
#define MOD 9901
using namespace std;

int putere(int a,int b){
  int p=1; ///a^b=a*a*...*a (de b ori)
  for(int i=1;i<=b;i++)
    p=(p*a)%MOD;
  return p;
}
int factorial(int n)
{
  if(n<=1) return 1;
  return n*factorial(n-1)%MOD;
}
int inv_mod(int x)
{
  return putere(x, MOD-2);
}
int comb(int n,int k)
{
  return factorial(n)*inv_mod(k)*inv_mod(n-k)%MOD;
}
int main() {
  int n,k;
  cin>>n>>k;
  cout<<comb(n,k);
 // cout<<factorial(n);
  ///cout<<putere(k, 10);
    //<<" "<<inv_mod(k)<<" "<<inv_mod(n-k);
}