import sys
input = sys.stdin.readline
N = int(input())
S = input().strip()
flag = [0 for _ in range(N)]
for i in range(N-2):
    if S[i]=="C" and S[i+1]=="P" and S[i+2]=="C":
        flag[i] = 1
s = "CPCTF"
dp = [[-1 for _ in range(5)] for _ in range(N+1)]
dp[0][0] = 0
for i in range(N):
    for j in range(5):
        if dp[i][j]==-1:
            continue
        if S[i]==s[j]:
            if j+1==5:
                dp[i+1][0] = max(dp[i+1][0], dp[i][j]+1)
            else:
                dp[i+1][j+1] = max(dp[i+1][j+1], dp[i][j])
        elif j==4 and flag[i]==1:
            dp[i+3][0] = max(dp[i+3][0], dp[i][j]+1)
        dp[i+1][0] = max(dp[i+1][0], dp[i][j])
ans = max(dp[N])
print(ans)