source_code: import java.util.Scanner;
  
  public class Tsk1 {
      static void metod() throws Exception {
          Scanner in = new Scanner(System.in);
          int n = in.nextInt();
          String s = in.next();
          String ss = s + s;
          int t = 0;
          for (int i = 0; i < n; i++) {
              if (s.charAt(i) == 'T') {
                  t++;
              }
          }
          if (t == 1 || t == n - 1) {
              System.out.println(0);
          } else {
              int sum = 0;
              for (int i = 0; i < t; i++) {
                  if (s.charAt(i) == 'T') {
                      sum++;
                  }
              }
              
              int max = sum;
              for (int i = 0; i < s.length(); i++) {
                  if (ss.charAt(i) == 'T') {
                      if (ss.charAt(i + t) == 'H') {
                          sum--;
                      }
                  } else {
                      if (ss.charAt(i + t) == 'T') {
                          sum++;
                          max = Math.max(max, sum);
                      }
                  }
              }
              System.out.println(t - max);
          }
      }
  
      public static void main(String[] args) throws Exception {
          Tsk1.metod();
      }
  }