N = int(input())
S = input()

T = ["CPCTF", "CPCTCPC"]

ret = 0

i = 0
while i < N:
    found = False
    for s in T:
        if i + len(s) <= N and S[i:i+len(s)] == s:
            ret += 1
            i += len(s)
            found = True
            break

    i += not found

print(ret)