source_code: import java.util.*;
  public class Main {
  
  	/**
  	 * @param args
  	 */
  	public static void main(String[] args) {
  		// TODO Auto-generated method stub
  		Scanner cin = new Scanner(System.in);
  		int n;
  		n = cin.nextInt();
  		String s = cin.next();
  		int ans = n;
  		int cntH = 0,cntT = 0;
  		for(int i=0;i<n;i++)
  		{
  			if(s.charAt(i)=='H')cntH++;
  		}
  		cntT = n - cntH;
  		for(int i=0;i+cntH<n;i++)
  		{
  			int tmp = 0;
  			for(int j=i;j<i+cntH;j++)
  				if(s.charAt(j)=='T')tmp++;
  			if(ans>tmp)ans = tmp;
  		}
  		for(int i=0;i+cntT<n;i++)
  		{
  			int tmp = 0;
  			for(int j=i;j<i+cntT;j++)
  				if(s.charAt(j)=='H')tmp++;
  			if(ans>tmp)ans = tmp;
  		}
  		System.out.println(ans);
  	}
  
  }
  