#include <bits/stdc++.h>
// mrrrow meeow :3
// go play vivid/stasis now! https://vividstasis.gay
#define fo(i, a, b) for (auto i = (a); i < (b); i++)
#define of(i, a, b) for (auto i = (b); i-- > (a);)
#define f first
#define s second
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define be(a) a.begin(), a.end()
using namespace std;
int ____init = [] {
ios::sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
return 0;
}();
int calc_add(int i) {
int r[3] = {0, 0, 0};
r[i / 1 % 3] = 1;
r[i / 3 % 3] = 1;
r[i / 9 % 3] = 1;
return r[0] + r[1] + r[2];
}
int full(int a) {
return a + a * 3 + a * 9;
}
int change(int i, int a) {
return i % 27 / 3 + a * 9;
}
int main() {
string s; cin >> s >> s;
array<int, 27> oo, on;
array<int, 729> o, n;
oo.fill(INT_MIN), o.fill(INT_MIN);
oo[full(s[0] == 'M' ? 0 : s[0] == 'F' ? 1 : 2)] = 1;
fo(i, 1, s.size()) {
int a = s[i] == 'M' ? 0 : s[i] == 'F' ? 1 : 2;
on.fill(INT_MIN), n.fill(INT_MIN);
fo(j, 0, 27) {
on[change(j, a)] = max(on[change(j, a)], oo[j] + calc_add(change(j, a)));
n[j + full(a) * 27] = max(n[j + full(a) * 27], oo[j] + 1);
n[full(a) + j * 27] = max(n[full(a) + j * 27], oo[j] + 1);
fo(k, 0, 27) {
n[change(j, a) + k * 27] = max(n[change(j, a) + k * 27], o[j + k * 27] + calc_add(change(j, a)));
n[k + change(j, a) * 27] = max(n[k + change(j, a) * 27], o[k + j * 27] + calc_add(change(j, a)));
}
}
swap(oo, on), swap(o, n);
}
int res = 0;
for (int i : oo) res = max(res, i);
for (int i : o) res = max(res, i);
cout << res;
}
