#include <bits/stdc++.h>   using namespace std;   const int MAX_N = 1e5 + 5;   char a[MAX_N];   int main() {     int N;     cin >> N;     scanf( %s , a + 1);     int cnt = 0;     for (int i = 1; i <= N; i++) {       if (a[i] ==  S  && a[i] >= 2 && a[i - 1] ==  G ) {         cnt++;       }     }     if (a[N] ==  G ) cnt++;     int len = 0, prelen = (cnt >= 2), ans = 0;     for (int i = 1; i <= N; i++) {       if (a[i] ==  G ) {         len++;         ans = max(ans, len + prelen);       }       if (a[i] ==  S ) {         if (2 <= i && i <= N - 1 && a[i - 1] ==  G  && a[i + 1] ==  G ) {           if (cnt == 2) {             prelen = len;           } else if (cnt >= 3) {             prelen = len + 1;           }         } else {           prelen = (cnt >= 2);         }         len = 0;       }     }     cout << ans << endl;     return 0;   }   