source_code: import java.io.*;
  import java.util.StringTokenizer;
  
  /**
   * Created by IntelliJ IDEA.
   * User: piyushd
   * Date: Dec 5, 2010
   * Time: 4:09:41 PM
   * To change this template use File | Settings | File Templates.
   */
  public class HamstersTigers {
      private BufferedReader in;
      private PrintWriter out;
      private StringTokenizer st;
  
  	int solve(String a, int k){
  		int n = a.length(), ret = 0;
  		int temp[] = new int[n];
  		for(int i = 0; i < n; i++) temp[(n + i - k) % n] = (a.charAt(i) == 'T') ? 1: 0;
  		int left = 0, right = n - 1;
  		while(left < right){
  			while(temp[left] == 0) left++;
  			while(temp[right] == 1) right--;
  			if(left < right){
  				int t = temp[left];
  				temp[left] = temp[right];
  				temp[right] = t;
  				ret++;
  			}
  		}
  		return ret;
  	}
  
      void solve() throws IOException {
  		int n = nextInt();
  		String a = next();
  		int ans = Integer.MAX_VALUE;
  		for(int fix = 0; fix < n; fix++){
  			ans = Math.min(ans, solve(a, fix));
  		}
  		out.println(ans);
      }
  
      HamstersTigers() throws IOException {
          in = new BufferedReader(new InputStreamReader(System.in));
          //in  = new BufferedReader(new InputStreamReader(new FileInputStream(new File("C://Users/piyushd/Desktop/codeforces/sample.txt"))));
          out = new PrintWriter(System.out);
  
          eat("");
  
          solve();
  
          in.close();
          out.close();
      }
  
      private void eat(String str) {
          st = new StringTokenizer(str);
      }
  
      String next() throws IOException {
          while (!st.hasMoreTokens()) {
              String line = in.readLine();
              if (line == null) {
                  return null;
              }
              eat(line);
          }
          return st.nextToken();
      }
  
      int nextInt() throws IOException {
          return Integer.parseInt(next());
      }
  
      long nextLong() throws IOException {
          return Long.parseLong(next());
      }
  
      double nextDouble() throws IOException {
          return Double.parseDouble(next());
      }
  
      public static void main(String[] args) throws IOException {
          new HamstersTigers();
      }
  }
  