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)