B1,B2

n,k=map(int,input().split())

line=input()

pos=k
f=0

if pos < 0:
    f = - pos
    pos = 0

for i in range(n-1):
    ig=line[i]

    if ig=='C':
        pos-=1
    if ig=='A':
        pos+=1

    if pos<0:
        f+=1
        pos=0
print(f)