#include <bits/stdc++.h>

using namespace std;
 
long long int fact(long long int number){
       long long int factorial=1;

       if(number==0 || number==1)
              return 1;

       else
      {
         for(long long int count=1;count<=number;count++)
        factorial=factorial*count;
      }
       return factorial;
    }

long long int ncr(long long int n,long long int r )
{
    long long int ans = fact(n)/fact(r) ;
    //cout<<ans;
    return ans;
    
}

long long int  countArray(long long int n,long long  int k,long long int x) {
  long long int a = ncr(n-4,k);
    return (((2*k)-3)+a);// Return the number of ways to fill in the array.
}

int main() {
  long long   int n;
  long long  int k;
  long long  int x;
    cin >> n >> k >> x;
    long long int answer = countArray(n, k, x);
    cout << answer << endl;
    return 0;
}