#include <bits/stdc++.h>
#pragma GCC optimize("O3")
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template <class c>
struct rge {
  c b, e;
};
template <class c>
rge<c> range(c i, c j) {
  return rge<c>{i, j};
}
template <class c>
auto dud(c* x) -> decltype(cerr << *x, 0);
template <class c>
char dud(...);
struct debug {
  template <class c>
  debug& operator<<(const c&) {
    return *this;
  }
};
const long long N = 1e5 + 5;
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n;
  cin >> n;
  string s;
  cin >> s;
  vector<long long> pref(n + 2), suff(n + 2);
  for (long long i = 1; i <= n; i++) {
    if (s[i - 1] == 'G') {
      pref[i] = 1;
      pref[i] += pref[i - 1];
    }
  }
  for (long long i = n; i >= 1; i--) {
    if (s[i - 1] == 'G') {
      suff[i] = 1;
      suff[i] += suff[i + 1];
    }
  }
  long long ans = 0;
  long long cnt = 0;
  for (long long i = 1; i <= n; i++) {
    if (s[i - 1] == 'G') cnt++;
    ans = max(ans, pref[i]);
  }
  for (long long i = 1; i <= n; i++) {
    if (s[i - 1] == 'S') {
      if (i == 4) {
        debug() << " ["
                << "pref[i - 1]"
                   ": "
                << (pref[i - 1])
                << "] "
                   " ["
                << "suff[i + 1]"
                   ": "
                << (suff[i + 1]) << "] ";
      }
      if (pref[i - 1] + suff[i + 1] < cnt)
        ans = max(ans, pref[i - 1] + suff[i + 1] + 1);
      else if (pref[i - 1] + suff[i + 1] == cnt) {
        ans = max(ans, pref[i - 1] + suff[i + 1]);
      }
    }
  }
  cout << ans << "\n";
  return 0;
}
