source_code: import java.util.Scanner;
  
  public class C {
      public static void main(String[] args) {
          Scanner s = new Scanner(System.in);
          int len = s.nextInt();
          s.nextLine();
          String l = s.nextLine();
          char[] ca = l.toCharArray();
          int h = 0;
          for (char c : ca)
              h += A(c);
          int cur = h;
          int i;
          for (i = 0; i < h; i++)
              cur -= A(ca[i]);
          int best = cur;
          while (i != h + len) {
              cur -= A(ca[i % len]);
              cur += A(ca[(i - h) % len]);
              best = best > cur ? cur : best;
              i++;
          }
          System.out.println(best);
      }
  
      public static int A(char x) {
          return x == 'H' ? 1 : 0;
      }
  }
  