import java.util.*;
import java.lang.*;
import java.io.*;
 
class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		int n, m, d;
		Scanner in = new Scanner(System.in);
		n = in.nextInt();
		m = in.nextInt();
		d = func(m, n); 
		System.out.print(d);
	}
	public static int func (int m, int n){
		if (m == 0 || m == n) return 1;
		else return func(m - 1, n - 1) + func(m, n - 1);
	}
}