#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  string s;
  int n;
  while (cin >> n) {
    cin >> s;
    int gold = 0, cnt = 0, prev = 0, ans = 0;
    for (auto ch : s) {
      if (ch == 'G')
        gold++, cnt++;
      else
        prev = cnt, cnt = 0;
      ans = max(ans, prev + cnt + 1);
    }
    ans = min(ans, gold);
    cout << ans << endl;
  }
  return 0;
}
