from functools import lru_cache
n = int(input())
m = int(input())
@lru_cache
def nPr(n,r):
    npr=1
    for i in range(n,n-r,-1):
        npr*=i
    return npr
sum = 0
if n-m >= 0:
  for i in range(n-m+1):
    sum += nPr(n,i)
print(sum)