N = int(input())
S = list(input())
Q = []
for i in range(N):
    if S[i] == "F":
        Q.append("C")
        Q.append("P")
        Q.append("C")
    else:
        Q.append(S[i])
        
N = len(Q)
ans = 0
stack = ["?", "?", "?", "?", "?", "?"]
for i in range(N):
    if Q[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
    stack.append(Q[i])
            
print(ans)