source_code: 
  import java.util.Scanner;
  
  /**
   *
   * @author igor_kz
   */
  public class C46 {
      public static void main(String[] args) {
          Scanner in = new Scanner(System.in);
          int number = in.nextInt();
          String s = in.next();
          int cH = 0;
          int n = s.length();
          for (int i = 0 ; i < n ; i++)
              if (s.charAt(i) == 'H') cH++;
          String ss = "";
          for (int i = 0 ; i < cH ; i++)
              ss += "H";
          for (int i = 0 ; i < n - cH ; i++)
              ss += "T";
          int res = Integer.MAX_VALUE;
          for (int i = 0 ; i < n ; i++) {
              int cur = countDifference(ss , s);
              res = Math.min(res , cur);
              ss = ss.substring(1) + ss.charAt(0);
          }
          System.out.println(res);
      }
  
      public static int countDifference(String ss, String s) {
          int cnt = 0;
          for (int i = 0 ; i < ss.length() ; i++)
              if (ss.charAt(i) != s.charAt(i)) cnt++;
          return cnt / 2;
      }
  }
  