1

n, k = map(int, input().split())
count_of_chocolade = 0
if k < 0:
    count_of_chocolade += abs(k)
    k = 0
stroke = input()
for elem in stroke[:-1]:
    if elem == "A":
        k += 1
    elif elem == "C":
        if k == 0:
            count_of_chocolade += 1
        else:
            k -= 1
if k < 0:
    count_of_chocolade += abs(k)
print(count_of_chocolade)