public class BankAccount {

    static int balance( int balance, int years) {
        //check for valid input
        if (years > 0 && balance > 0 && balance < 50001) {
            double rate = 0.5;
            if (balance > 1000) {
                rate = 1.5;
            }
            if (balance > 10000) {
                rate = 2.5;
            }
            //run calculation
            return (int)Math.round(balance * Math.pow((1+(double)rate/100), years));
        } else {
            //invalid input
            return -1;
        }
    }

}