source_code: /*
   * To change this template, choose Tools | Templates
   * and open the template in the editor.
   */
  
  
  import java.util.* ;
  import java.io.* ;
  import java.math.* ;
  /************************
   *                      *
   *    Lord Klotski      *
   *                      *
   ***********************/
  public class C
  {
      static int[] arr ; static int L ;
      public static void rotate()
      {
          int tmp = arr[0] ;
          for (int i = 1 ; i < L ; i ++)
              arr[i-1] = arr[i] ;
          arr[L-1] = tmp ;
      }
  
      public static void main(String[] args)
      {
          Scanner input = new Scanner(System.in) ;
  
          L = input.nextInt() ; String s = input.next() ;
          arr = new int[L]; for (int i = 0 ; i < L ; i ++) {arr[i] = s.charAt(i) == 'H' ? 1 : 0 ;}
  
          // want to find longest sequence of 1s
          // then rotate to head
          int count = 99999 ;
          for (int A = 0; A < L ; A ++)
          {
              int[] tmp = new int[L] ; System.arraycopy(arr, 0, tmp, 0, arr.length);
              int ans = 0 ;
              for (int i = 0 ; i < L ; i ++)
              {
                  if (tmp[i] == 1) continue ;
                  for (int j = L-1 ; j > i ; j --)
                  {
                      if (tmp[j] == 0) continue ;
                      ans ++ ;
                      tmp[i] = 1 ; tmp[j] = 0 ;
                      //System.out.println("SWAP " + i + " " + j);
                      //for (int k = 0 ; k < L ; k ++)
                      //    System.out.print(arr[k]);
                      //System.out.println("");
                      break;
                  }
              }
              count = Math.min(count,ans) ;
              rotate() ;
          }
          // rotate until j is at the front
          System.out.println(count);
  
      }
  }
  