n, k = map(int, input().split())
sp = list(filter(lambda x: x != 'B', list(input())))
kol = 0
for _ in range(sp.count('A')):
    x = sp.index('A')
    if sp[x:].count('C') != 0:
        del sp[sp[x:].index('C')]
        del sp[x]
    else:
        sp = sp[:sp.index('A')]
        break
print(len(sp))