N=int(input())
S=input()
T=list(S)
for i in range(N-3+1):
    if S[i:i+3]=="CPC":
        T[i]="F";T[i+1]="F";T[i+2]="F"
T="".join(T)
dp=[[0,0] for _ in range(N+1)]
for i in range(5,N+1):
    if S[i-5:i]=="CPCTF":
        dp[i][0]=dp[i-1][0]+1
    else:
        dp[i][0]=dp[i-1][0]
    if S[i-5:i-1]=="CPCT" and T[i-1]=="F":
        dp[i][1]=max(dp[i-1][0]+1,dp[i-1][1]+1)
    else:
        dp[i][1]=dp[i-1][1]
print(max(dp[N]))