source_code: import java.io.BufferedReader;
  import java.io.InputStreamReader;
  import java.io.PrintWriter;
  import java.io.StreamTokenizer;
  
  public class B {
      private static StreamTokenizer in;
      private static PrintWriter out;
      
      private static int nextInt() throws Exception{
          in.nextToken();
          return (int)in.nval;
      }
      
      private static String nextString() throws Exception{
          in.nextToken();
          return in.sval;
      }
      
      static{
          in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
          out = new PrintWriter(System.out);
      }
      
      public static void main(String[] args)throws Exception{
          int n = nextInt();
          char[] c = nextString().toCharArray();
          
          int tc = 0, hc = 0;
          for(int i = 0;i<c.length; i++){
              if(c[i] == 'T')tc++; else hc++;
          }
  //      char g = 'T';
  //      if(tc > hc){
  //          tc = hc;
  //          g = 'H';
  //      }
          
          int max = -1;
          int pos = 0;
          for(int i = 0; i<c.length; i++){
              int a = 0;
              for(int j = 0; j<tc;j++){
                  int k = i+j;
                  if(k>=n)k-=n;
                  if(c[k] == 'T'){
                      a++;
                  }
              }
              if(a>max){
                  max = a;
                  pos = i;
              }
          }
          int min1 = tc - max;
          
          max = -1;
          pos = 0;
          for(int i = 0; i<c.length; i++){
              int a = 0;
              for(int j = 0; j<hc;j++){
                  int k = i+j;
                  if(k>=n)k-=n;
                  if(c[k] == 'H'){
                      a++;
                  }
              }
              if(a>max){
                  max = a;
                  pos = i;
              }
          }
          int min2 = hc - max;
          
          out.println(Math.min(min1, min2));
          out.flush();
      }
  }
  