from itertools import accumulate


def flt(x):
    if x == 'A':
        return 1
    elif x == 'C':
        return -1
    elif x == 'B':
        return 0


n, k = map(int, input().split())
students = list(accumulate(map(flt, input())))
for i in range(n):
    if students[i] < 0:
        print(students[-1] - students[i])
        exit()
print(0)