source_code: import java.util.Scanner;
  
  
  public class ProblemC {
  
      public static void main(String[] args) {
          ProblemC problem = new ProblemC();
          problem.solve();
      }
  
      private void solve() {
          Scanner sc = new Scanner(System.in);
          int n = sc.nextInt();
          String s = sc.next();
          int ret = n;
          int toth = 0;
          int tott = 0;
          for (int j = 0; j < n; j++) {
              if (s.charAt(j) == 'H') {
                  toth++;
              } else {
                  tott++;
              }
          }
          for (int j = 0; j < n; j++) {
              int cnth = 0;
              for (int k = 0; k < toth; k++) {
                  int pos = (j + k) % n;
                  if (s.charAt(pos) == 'H') {
                      cnth++;
                  }
              }
              int makeh = toth - cnth;
              ret = Math.min(ret, makeh);
          }
          System.out.println(ret);
      }
  
  }
  