source_code: import java.io.PrintWriter;
  import java.util.*;
  
  
  public class Main {
  	public static void main(String[] args) {
  		Scanner in = new Scanner(System.in);
  		PrintWriter out = new PrintWriter(System.out);
  		
  		// 1 = H, 0 = T
  		
  		int n = in.nextInt();
  		String line = in.next();
  		int h = 0;
  		for (int i = 0; i < line.length(); i++) {
  			if(line.charAt(i)=='H') h++;
  		}
  		line = line + line;
  		
  		int min = Integer.MAX_VALUE;
  		for (int i = 0; i < n; i++) {
  			int ans = 0;
  			for (int j = i; j < i+h; j++) {
  				if(line.charAt(j)!='H') ans++;
  			}
  			if(min>ans) min = ans;
  		}
  		
  		out.print(min);
  		
  		
  		
  		
  		in.close();
  		out.close();
  	}
  
  }
  