import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class Demo {

   private static String a= "am";

   private static String b= "The am ss am te.";

   private static String c = "mm";

   public static void main(String[] args) {

      Pattern pattern = Pattern.compile(a);

      Matcher matcher = pattern.matcher(b);

      b= matcher.replaceFirst(c);

      System.out.println(b);

   }

}