def Pulscoross(n):
    count = 1
    for i in range(1, n+1):
        sum = i*count
        count=sum
    return count
   
def Twocross(x , y):
     total1 = Pulscoross(x)
     total2 = Pulscoross(y)
     total = int(total1/total2)
     return total

num1,num2 = map(int,input().split())
if(num1 >= num2):
    print(Twocross(num1,num1-num2))
else:
    print(0)