#include <iostream>
#include <fstream>
using namespace std;
int fact(int n)
{
    if(n==0)
    return 1;
    else
    return n*fact(n-1);
}
int main()
{
   ifstream fin("pascal.in");
   ofstream fout("pascal.out");
   int a,b;
   fin>>a>>b;
   fout<<fact(a-1)/(fact(a-b)*fact(b-1));
   fin.close();
   fout.close();
   return 0;
}