n = int(input())
S = input()
dp = [0] * (n + 1)
for i in range(n):
    dp[i + 1] = dp[i]
    if i >= 4 and S[i - 4 : i + 1] == "CPCTF":
        dp[i + 1] = max(dp[i + 1], dp[i - 4] + 1)
    if i >= 6 and S[i - 6 : i + 1] == "CPCTCPC":
        dp[i + 1] = max(dp[i + 1], dp[i - 6] + 1)

print(dp[n])