text: def combination(n, r):
      if n < r:
          return 0
      if r == 0:
          return 1
  
      tmp_n = 1
      for i in range(r):
          tmp_n *= n - i
      tmp_r = 1
      for i in range(r):
          tmp_r *= r - i
      return tmp_n // tmp_r
  n, r = map(int, input().split())
  print(combination(n, r))
  
  def cmb(n, r):
      if n - r < r: r = n - r
      if r == 0: return 1
      if r == 1: return n
  
      numerator = [n - r + k + 1 for k in range(r)]
      denominator = [k + 1 for k in range(r)]
  
      for p in range(2,r+1):
          pivot = denominator[p - 1]
          if pivot > 1:
              offset = (n - r) % p
              for k in range(p-1,r,p):
                  numerator[k - offset] /= pivot
                  denominator[k] /= pivot
  
      result = 1
      for k in range(r):
          if numerator[k] > 1:
              result *= int(numerator[k])
  
      return result