f = open('INPUT.TXT')
n, m = map(int, f.readline().split())
f.close()

def factorial(x):
    if x <= 1:
        return 1
    result = 1
    for i in range(2, x + 1):
        result = result * i
    return result

def binomial(n, k):
    if k > n or k < 0:
        return 0
    return factorial(n) // (factorial(k) * factorial(n - k))

count = 0
for k in range(m, n + 1):
    count = count + binomial(n, k)

f = open('OUTPUT.TXT', 'w')
f.write(str(count))
f.close()