source_code: import java.util.*;
  import java.lang.*;
  import java.io.*;
  import java.math.*;
  
  public class Main { 
      public static StreamTokenizer in;
      public static PrintStream out;
      public static BufferedReader br;
  
      public static String readString() throws IOException {
          in.nextToken();
          return  in.sval;
          }
  
      public static double readDouble() throws IOException {
          in.nextToken();
          return in.nval;
          }
  
      public static int readInt() throws IOException {
          in.nextToken();
          return (int) in.nval;
      }
      
      public static String readLine() throws IOException {
      return br.readLine();
      }
      
      public static int genans(String ss) {
      	
      	int n = ss.length();
      	char[] s = ss.toCharArray();
      	int res = 0;
      	while (true) {
      		int firstT = -1;
      		for (int i=0; i<n; i++)
      			if (s[i]=='T') { firstT = i; break; }
      		
      		int lastH = -1;
      		for (int i=n-1; i>=0; i--)
      			if (s[i]=='H') { lastH=i; break; }
      		
      		if (firstT<lastH) {
      			res++;
      			s[firstT] = 'H';
      			s[lastH] = 'T';
      		} else break;
      		
      	}	
      	return res;
      }
      
      public static void main(String[] args) throws IOException {
  
          in = new StreamTokenizer(new InputStreamReader (System.in) );
          br = new BufferedReader(new InputStreamReader(System.in));
          out = new PrintStream(System.out);
  
          readLine();
          String s = readLine();
          int n = s.length();
          String kk = s;
          int ans = n*100;
          for (int tr=0; tr<n+2; tr++) {
          	String kk2 = "";
          	for (int i=1; i<n; i++) kk2 = kk2 +kk.charAt(i);
          	kk2 = kk2 + kk.charAt(0);
          	kk = kk2;
          
          int cur = genans(kk);
          //out.println(kk+" "+cur);
          if (cur<ans) ans = cur;
          }
          
          out.println(ans);
  
      }
      
  
  }
  
  