#include <bits/stdc++.h> using namespace std; #define OPTM ios_base::sync_with_stdio(0); cin.tie(0); #define INF int(1e9+7) #define ln '\n' #define ll long long #define ull unsigned long long #define ui unsigned int #define us unsigned short #define FOR(i,s,n) for (int i = s; i < n; i++) #define FORR(i,n,s) for (int i = n; i > s; i--) #define FORX(u, arr) for (auto u : arr) #define PB push_back #define in(v,x) (v.find(x) != v.end()) #define F first #define S second #define PII pair<int, int> #define PLL pair<ll, ll> #define UM unordered_map #define US unordered_set #define PQ priority_queue #define ALL(v) v.begin(), v.end() const ll LLINF = 1e18+1; #define int long long const int MAXN = 1e5+1; int n; int s[MAXN]; const string abc = "MBF"; UM<char,int> mp; int dp[2][4][4][4][4]; int calc(int a, int b, int c) { US<int> tmp; if (a) tmp.insert(a); if (b) tmp.insert(b); if (c) tmp.insert(c); return tmp.size(); } signed main() { OPTM; FOR(i,0,3) mp[abc[i]] = i+1; cin >> n; FOR(i,0,n) { char c; cin >> c; s[i] = mp[c]; } FOR(a,0,4) { FOR(b,0,4) { FOR(c,0,4) { FOR(d,0,4) { dp[0][a][b][c][d] = dp[1][a][b][c][d] = -LLINF; } } } } dp[0][0][0][0][0] = 0; FOR(i,0,n) { int x = s[i]; FOR(a,0,4) { FOR(b,0,4) { FOR(c,0,4) { FOR(d,0,4) { if (dp[0][a][b][c][d] == -LLINF) continue; dp[1][b][x][c][d] = max(dp[1][b][x][c][d], dp[0][a][b][c][d]+calc(a,b,x)); dp[1][a][b][d][x] = max(dp[1][a][b][d][x], dp[0][a][b][c][d]+calc(c,d,x)); } } } } FOR(a,0,4) { FOR(b,0,4) { FOR(c,0,4) { FOR(d,0,4) { dp[0][a][b][c][d] = dp[1][a][b][c][d]; dp[1][a][b][c][d] = -LLINF; } } } } } int res = 0; FOR(a,0,4) { FOR(b,0,4) { FOR(c,0,4) { FOR(d,0,4) { res = max(res, dp[0][a][b][c][d]); } } } } cout << res; }