import java.util.Stack;
public class Question5 {

	/*Stacks and Queues: Write a program evaluate arithmetical expressions
	 *  that use + and * applied to nonnegative integer arguments. Expressions are in
	 *  reverse-Polish notation, e.g., 3 4 + 5 *, 1 3 + 5 7 + *. (from EPI)
	 */

	public int evalArimathical(String s) {
		int answer = 0;
		char[] exp = s.toCharArray();
		int length = s.length();

		Stack<Integer> eval = new Stack<Integer>();
		StringBuffer buff = new StringBuffer();

		for (int i = 0; i < length; i++) {

			if (exp[i] != '+' && exp[i] != '-' && exp[i] != '*' && exp[i] != '/') {
				// In case if there are more that 1 digit of the number

				buff.delete(0, buff.length());
                // There may be more than one digits in number
                while (i < exp.length && exp[i] >= '0' && exp[i] <= '9')
                    buff.append(exp[i++]);

             if(buff.toString() != null) {
                  eval.push(Integer.parseInt(buff.toString()));
                }

				// not a number do calculation
			} else {
				int a = eval.pop();
			    int b = eval.pop();

				switch (exp[i]) {
				case '+':
					answer = a + b;
					break;
				case '-':
					answer = a - b;
					break;
				case '*':
					answer = a * b;
					break;
				case '/':
					answer = b/a;
					break;
				default:
				}

				eval.push(answer);
			}

		}

	return answer;

}

}