n = int(input())
s = input().strip()
L = 0
def h_agct(s):
    for ch in s:
        if ch in "AGCT":
            return True

    return False



while h_agct(s) == True:
    c = 0
    for ch in s:
        if ch in "AGCT":
            c += 1
    if c > 0:
        s = s[:c-1] + s[c:]
        L = L + 1
print(L)