source_code: import java.io.*;
  import java.util.*;
  
  public class Main {
  	private static boolean _READ_FROM_FILE = System.getProperty("ONLINE_JUDGE") == null;
  	private static Scanner in;
  	private static void core() {
  		int n = in.nextInt();
  		ArrayList<Character> all = new ArrayList<Character>();
  		for (char ch : in.next().toCharArray()) {
  			all.add(ch);
  		}
  		
  		int res = Integer.MAX_VALUE;
  		for (int i = 0; i < n; i++) {
  			int now = calc(all);
  			res = Math.min(res, now);
  			all.add(all.get(0));
  			all.remove(0);
  		}
  		System.out.println(res);
  	}
  	private static int calc(ArrayList<Character> all) {
  		int nh = 0;
  		for (char ch: all) {
  			if (ch == 'H')
  				++nh;
  		}
  		int r1 = 0;
  		for (int i = 0; i < nh; i++) {
  			if (all.get(i) != 'H')
  				++r1;
  		}
  		
  		int nt = all.size() - nh;
  		int r2 = 0;
  		for (int i = 0; i < nt; i++) {
  			if (all.get(i) != 'T')
  				++r2;
  		}
  		return Math.min(r1, r2);
  	}
  	static void debug(Object...os) {
  		System.out.println(Arrays.deepToString(os));
  	}
  	public static void main(String[] args) throws FileNotFoundException {
  		if (_READ_FROM_FILE)
  			System.setIn(new FileInputStream("in.in"));
  		in = new Scanner(System.in);
  		core();
  	}
  }
  