n, m = map(int, input().split())
def factorial(a,res):
if a == 1:
return res
else:
res=res*a
return factorial(a-1,res)
up=factorial(n,1)
d1=factorial(m,1)
d2=factorial(n-m,1)
#print("up:",up,"d1:",d1,"d2",d2)
print(up//(d1*d2))