kolvo, nastroenie = map(int, input().split())
st = list(input())
#st = list(filter(lambda a: a != 'B', st))
if nastroenie >= 0:
    cho = 0
else:
    cho = -nastroenie
    nastroenie = 0

for i in range(len(st)):
    if st[i] == 'A':
        nastroenie += 1
    elif st[i] == 'C':
        nastroenie -= 1
        #print(nastroenie)
    if nastroenie < 0 and i != len(st) - 1:
        cho += 1
        nastroenie += 1
# if st[-1] == 'C' and cho != 0:
#     print(cho - 1)
# else:
print(cho)