source_code: import java.io.*;
  import java.util.*;
  
  
  public class HamstersAndTigers
  {
  	Scanner in;
  	PrintWriter out;
  	
  	HamstersAndTigers()
  	{
  		in = new Scanner(System.in);
  		out = new PrintWriter(System.out);
  	}
  	
  	HamstersAndTigers(String i, String o) throws FileNotFoundException
  	{
  		in = new Scanner(new File(i));
  		out = new PrintWriter(new File(o));
  	}
  	
  	public void finalize()
  	{
  		out.flush();
  		in.close();
  		out.close();
  	}
  	
  	void solve()
  	{
  		int i = 0,
  			h = 0,
  			n = in.nextInt();
  		
  		String buf = "";
  		char[] ht = in.next().toCharArray();
  		
  		for(i = 0; i < n; ++i)
  			if(ht[i] == 'H')
  				++h;
  		
  		for(i = 0; i < h; ++i)
  			buf += 'H';
  		
  		for(i = 0; i < n - h; ++i)
  			buf += 'T';
  		
  		int diff = (1 << 28);
  		for(i = 0; i < n; ++i)
  		{
  			int tmp = 0;
  			
  			for(int j = 0; j < n; ++j)
  				if(buf.charAt(j) != ht[(i + j) % n])
  					++tmp;
  			
  			diff = Math.min(tmp, diff);
  		}
  		
  		out.println(diff / 2);
  	}
  	
  	public static void main(String[] args) throws FileNotFoundException
  	{
  		HamstersAndTigers t = new HamstersAndTigers();
  		t.solve();
  		t.finalize();
  	}
  }
  
  