source_code: import java.io.FileNotFoundException;
  import java.math.BigInteger;
  import java.util.Arrays;
  import java.util.Scanner;
  
  public class Main
  {
      static final double eps=1e-10;
      public static void main(String[] args) throws FileNotFoundException
      {
          new Main().solve();
      }
      public void solve() throws FileNotFoundException
      {
          Scanner cin=new Scanner(System.in);
          int n;
          n=cin.nextInt();
          String s;
          s=cin.next();
          int ans=Integer.MAX_VALUE;
          int h=0,t=0;
          for(int i=0;i<s.length();i++)
          {
              if(s.charAt(i)=='H')
                  h++;
              else if(s.charAt(i)=='T')
                  t++;
          }
          ans=Math.min(ans,fun(s,'H',h));
          ans=Math.min(ans,fun(s,'T',t));
          System.out.println(ans);
      }
      public int fun(String s,char c,int num)
      {
          int ans=Integer.MAX_VALUE;
          int ret=num;
          for(int i=0;i<num;i++)
          {
              if(s.charAt(i)==c)
              {
                  ret--;
              }
          }
          ans=ret;
          for(int i=0;i+num<s.length();i++)
          {
              if(s.charAt(i)!=c)
                  ret--;
              if(s.charAt(i+num)!=c)
              {
                  ret++;
              }
              ans=Math.min(ans, ret);
          }
          return ans;
      }
  }
  