source_code: //package round43;
  
  import java.io.PrintWriter;
  import java.util.Arrays;
  import java.util.Scanner;
  
  public class C {
  	Scanner in;
  	PrintWriter out;
  	String INPUT = "";
  	
  	void solve()
  	{
  		int n = ni();
  		char[] x = in.next().toCharArray();
  		int t = 0;
  		for(int i = 0;i < n;i++){
  			if(x[i] == 'T'){
  				t++;
  			}
  		}
  		
  		int min = 9999;
  		for(int i = 0;i < n;i++){
  			int y = 0;
  			for(int j = i;j < i + t;j++){
  				if(x[j % n] == 'T'){
  					y++;
  				}
  			}
  			min = Math.min(min, t - y);
  		}
  		out.println(min);
  	}
  	
  	void run() throws Exception
  	{
  		in = INPUT.isEmpty() ? new Scanner(System.in) : new Scanner(INPUT);
  		out = new PrintWriter(System.out);
  
  		solve();
  		out.flush();
  	}
  	
  	
  	public static void main(String[] args) throws Exception
  	{
  		new C().run();
  	}
  	
  	int ni() { return Integer.parseInt(in.next()); }
  	void tr(Object... o) { if(INPUT.length() != 0)System.out.println(o.length > 1 || o[0].getClass().isArray() ? Arrays.deepToString(o) : o[0]); }
  }
  