def maxConsecutiveStrings(S: str) -> int:
    n = len(S)
    last_c = None
    count = 0
    max_count = 0
    for i in range(n):
        if S[i] == 'C':
            if last_c == 'T':
                count -= 1
            count += 1
        else:
            last_c = S[i]
        if S[i] == 'F':
            max_count = max(max_count, count)
            count = 0
    return max_count


N = int(input())
s = input()
print(maxConsecutiveStrings(s))