#include<bits/stdc++.h> using namespace std; #pragma GCC optimize ("Ofast") typedef long long ll; typedef pair<ll , ll> pll; const ll maxn = 4e5 + 17; string s; vector<ll> a , b; ll ps[maxn]; int main(){ ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0); ll n; cin>>n>>s; for(ll i = 0 ; i < (n << 1) ; i++){ if(s[i] == 'B'){ a.push_back(i); } else { b.push_back(i); } } ps[0] = (s[0] == 'B'); for(ll i = 1 ; i < (n << 1) ; i++){ ps[i] = ps[i - 1] + (s[i] == 'B'); } ll res = 0; for(ll k = 0 ; k < n ; k++){ ll cur = 0; for(ll t = 0 ; t < n ; t++){ ll i = a[t] , j = b[(t + k) % n]; if(i < j){ ll h1 = ps[j] - ps[i] , h0 = j - i - 1 - h1 , b0 = n - 1 - h0 , h = max(0ll , h1 - b0); cur += j - i - 1 - (h << 1); } else { ll d = (n << 1) - (i - j + 1) , h1 = n - ps[i] + ps[j] , h0 = d - h1 , b0 = n - 1 - h0 , h = max(0ll , h1 - b0); cur += d - (h << 1); } } cur >>= 1; res = max(res , cur); } cout<<res<<'\n'; return 0; }