#include <bits/stdc++.h> using namespace std; int n; string s; map<char, int> mp; int dp[2][4][4][4][4]; int chk(int a, int b, int c){ vector<bool> v(4, false); v[a] = 1; v[b] = 1; v[c] = 1; return v[1] + v[2] + v[3]; } signed main(){ ios_base::sync_with_stdio(false); cin.tie(NULL); cin >> n >> s; s = ' ' + s; mp['M'] = 1; mp['B'] = 2; mp['F'] = 3; for(int i = 0;i<2;i++){ for(int j = 0;j<4;j++){ for(int k = 0;k<4;k++){ for(int g = 0;g<4;g++){ for(int f = 0;f<4;f++){ dp[i][j][k][g][f] = -2e9; } } } } } dp[0][0][0][0][0] = 0; for(int i = 1;i<=n;i++){ int id = mp[s[i]]; for(int j = 0;j<4;j++){ for(int k = 0;k<4;k++){ for(int g = 0;g<4;g++){ for(int f = 0;f<4;f++){ dp[i&1][id][j][g][f] = max(dp[i&1][id][j][g][f], dp[1-(i&1)][j][k][g][f] + chk(id, j, k)); dp[i&1][j][k][id][g] = max(dp[i&1][j][k][id][g], dp[1-(i&1)][j][k][g][f] + chk(id, g, f)); } } } } } int ans = 0; for(int j = 0;j<4;j++){ for(int k = 0;k<4;k++){ for(int g = 0;g<4;g++){ for(int f = 0;f<4;f++){ ans = max(ans, dp[n&1][j][k][g][f]); } } } } cout << ans; }