n=int(input())
st=[]
s=input()
ans=0

i=0
while i<n:
    # print(st)
    if len(st)>=4 and "".join(st[len(st)-4:])=="CPCT":
        if s[i]=="F":
            for i in range(4):
                st.pop()
            ans+=1
            i+=1
        elif i+3<=n and s[i:i+3]=="CPC":
            for i in range(4):
                st.pop()
            ans+=1
            i+=3
        else:
            st.append(s[i])
            i+=1
    else:
        st.append(s[i])
        i+=1
print(ans)