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

ans = 0
stack = ["?", "?", "?", "?", "?", "?"]
for i in range(N):
    if S[i] == "C":
        if stack[-6:] == ["C", "P", "C", "T", "C", "P"]:
            ans += 1
            stack.pop()
            stack.pop()
            stack.pop()
            stack.pop()
            stack.pop()
            stack.pop()
            continue
    if S[i] == "F":
        if stack[-4:] == ["C", "P", "C", "T"]:
            ans += 1
            stack.pop()
            stack.pop()
            stack.pop()
            stack.pop()
            continue
        
    stack.append(S[i])
            
print(ans)