source_code: import java.util.*;
  import java.io.*;
  
  public class Solution {
      public static void main(String[] args) throws Exception {
          Scanner sc = new Scanner(new InputStreamReader(System.in));
          int n = sc.nextInt();
          String s = sc.next();
          sc.close();
          
          int cH = 0;
          for (int i=0; i < s.length(); i++)
              if (s.charAt(i) == 'H')
                  cH++;
          
          int best = cH;
          
          for (int st=0; st < s.length(); st++) {
              int cur = st;
              int cnt = cH;
              for (int i=0; i < cH; i++) {
                  if (s.charAt(cur) == 'H')
                      cnt--;
                  cur++;
                  if (cur == s.length()) cur = 0;
              }
              best = Math.min(best, cnt);
          }
          
          System.out.println(best);
      }
  }
  