n,k = input().split()
n = int(n)
k = int(k)
stud = input()
choco = 0
for i in range(n):
    if k<0:
        choco +=(-k)
        k = 0
    if stud[i]=="A":
        k+=1
    if stud[i] =="C":
        k -=1
print(choco)