#include <bits/stdc++.h>

using namespace std;
using ll = long long;

constexpr ll mod = 998244353;

template<ll mod>
struct Mint {
  using M=Mint; ll v;
  M& put(ll x) { v=(x<mod)?x:x-mod; return *this; }
  Mint(ll x=0) { put(x%mod+mod); }
  M operator+(M m) {return M().put(v+m.v);}
  M operator-(M m) {return M().put(v+mod-m.v);}
  M operator*(M m) {return M().put(v*m.v%mod);}
  M operator/(M m) {return M().put(v*m.inv().v%mod);}
// BEGIN IGNORE
  M operator+=(M m) { return put(v+m.v); }
  M operator-=(M m) { return put(v+mod-m.v); }
  M operator*=(M m) { return put(v*m.v%mod); }
  M operator/=(M m) { return put(v*m.inv().v%mod); }
// END IGNORE
  bool operator==(M m) { return v==m.v; }
  M pow(ll m) const {
    M x=v, res=1;
    while (m) {
      if (m&1) res=res*x;
      x=x*x; m>>=1;
    }
    return res;
  }
  M inv() { return pow(mod-2); }
};

using mint = Mint<mod>;

int main(){

  cin.tie(0);
  cin.sync_with_stdio(0);

  int n;
  string s;
  cin >> n >> s;
  vector<int> dp(5, -1e9);
  dp[0] = 0;
  for(int i = 0; i < n; ++i){
    vector<int> nex(5, -1e9);
    nex[0] = *max_element(dp.begin(), dp.end());
    if(s.substr(i, 3) == "CPC" || s[i] == 'F'){
      nex[0] = max(nex[0], dp[4] + 1);
    }
    string t = "CPCT";
    for(int j = 0; j < 4; ++j){
      if(s[i] == t[j]){
        nex[j + 1] = max(nex[j + 1], dp[j]);
      }
    }
    swap(nex, dp);
  }
  cout << *max_element(dp.begin(), dp.end()) << endl;
}