#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
using uint = unsigned;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
template<class T> using pq = priority_queue<T, vector<T>, greater<T>>;
const ll LINF=0x1fffffffffffffff;
const ll MINF=0x7fffffffffff;
const int INF=0x3fffffff;
const int MOD=1000000007;
const int MOD2=998244353;
const ld EPS=1e-9;
const ld PI=3.14159265358979323846;
const ll dx[] = {0, 1, 0, -1, 1, -1, 1, -1};
const ll dy[] = {1, 0, -1, 0, 1, 1, -1, -1};
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (int i = m; i < (n); i++)
#define per(i, b) per2(i, 0, b)
#define per2(i, a, b) for (int i = int(b) - 1; i >= int(a); i--)
#define ALL(c) (c).begin(), (c).end()
#define SZ(x) ((int)(x).size())
#define nep(x) next_permutation(ALL(x))
template <class T>
using V = vector<T>;
template <class T>
using VV = V<V<T>>;
template <class T>
using VVV = V<VV<T>>;
template <class T>
using VVVV = V<VVV<T>>;
template <class T>
using V_p = V<pair<T,T>>;
template <class T>
using n_pq = priority_queue<T>;
template <class T>
using r_pq = priority_queue<T,vector<T>,greater<T>>;
template <class T>ostream &operator<<(ostream &o,const vector<T>&v)
{o<<"{";for(int i=0;i<(int)v.size();i++)o<<(i>0?", ":"")<<v[i];o<<"}";return o;}
template <class T>ostream &operator<<(ostream &o,const deque<T>&v)
{o<<"{";for(int i=0;i<(int)v.size();i++)o<<(i>0?", ":"")<<v[i];o<<"}";return o;}
template <class T>ostream &operator<<(ostream &o,const set<T>&v)
{o<<"{";for(auto i:v)o<<" "<<i;o<<"}";return o;}
ll pow_ll(ll x, ll n) {
    long long ret = 1;
    while (n > 0) {
        if (n & 1) ret *= x;  // n の最下位bitが 1 ならば x^(2^i) をかける
        x *= x;
        n >>= 1;  // n を1bit 左にずらす
    }
    return ret;
}


////////////////////////////////////////////////////

int main() {
    ll N;
    cin >> N;
    string S;
    cin >> S;
    VV<ll> dp(N+1,V<ll>(6,-1));
    dp[0][0] = 0;
    ll max_case;
    max_case = 0;
    rep(i,N) {
        dp[i+1][0] = max(dp[i+1][0],dp[i][0]);
        if (S[i] == 'C') {
            dp[i+1][1] = dp[i][0];
            if (dp[i][2] >= 0) {
                dp[i+1][3] = max(dp[i+1][3],dp[i][2]);
            }
        }
        else if (S[i] == 'P') {
            if (dp[i][1] >= 0) {
                dp[i+1][2] = max(dp[i+1][2],dp[i][1]);
            }    

        }
        else if (S[i] == 'T') {
            if (dp[i][3] >= 0) {
                dp[i+1][4] = max(dp[i+1][4],dp[i][3]);
            }    

        }
        else if (S[i] == 'F') {
            if (dp[i][4]>=0) {
                dp[i+1][0] = max(dp[i+1][0],dp[i][4]+1);
            }

        }

        if (i+3<=N && dp[i][4] >= 0) {
            if (S.substr(i,3) == "CPC") {
                dp[i+3][0] = max(dp[i+3][0],dp[i][4]+1);

            }
        }
    }
    ll ans = 0;
    rep(i,N+1) {
        rep(j,6) {
            ans = max(ans,dp[i][j]);


        }
    }
    cout << ans << endl;
}