import java.util.StringTokenizer;
import java.util.Stack;


public class Calculator {

	static int precedence(char op) {
		switch (op) {
		case '+':
		case '-':
			return 5;
		case '*':
		case '/':
			return 10;
		default:
			throw new IllegalArgumentException("invalid operator");				
		}
	}

	public static String infixToPostfix(String infix) {
		StringTokenizer tokenizer = new StringTokenizer(infix);
		String postfix = "";
		Stack opStack = new Stack();

		while (tokenizer.hasMoreTokens()) {
			String token = tokenizer.nextToken();
			char c = token.charAt(0);
			if (Character.isDigit(c)) {
				postfix += (token + " ");
			}
			else {
				while (!opStack.empty()) {
					char top = ((Character)opStack.peek()).charValue();
					if (precedence(top) >= precedence(c)) {
						postfix += (top + " ");
						opStack.pop();
					}
					else {
						break;
					}
				}

				opStack.push(new Character(c));
			}
		}

		while (!opStack.empty()) {
			char top = ((Character)opStack.pop()).charValue();
			postfix += (top + " ");
		}

		return postfix;
	}

	public static int evalPostfix(String postfix) {
		StringTokenizer tokenizer = new StringTokenizer(postfix);
		Stack valStack = new Stack();

		while (tokenizer.hasMoreTokens()) {
			String token = tokenizer.nextToken();
			char c = token.charAt(0);
			if (Character.isDigit(c)) {
				valStack.push(new Integer(token));
			}
			else {
				int rightVal = ((Integer)valStack.pop()).intValue();
				int leftVal = ((Integer)valStack.pop()).intValue();
				int rslt;

				switch (c) {
				case '+': rslt = leftVal + rightVal; break;
				case '-': rslt = leftVal - rightVal; break;
				case '*': rslt = leftVal * rightVal; break;
				case '/': rslt = leftVal / rightVal; break;
				default:
					throw new IllegalArgumentException("invalid postfix expression");
				}

				valStack.push(new Integer(rslt));
			}
		}

		int rslt = ((Integer)valStack.pop()).intValue();
		if (!valStack.empty()) {
			throw new IllegalArgumentException("invalid postfix expression");
		}

		return rslt;
	}

	public static void main(String[] args) {
		String infix = args[0];
		String postfix = infixToPostfix(infix);
		System.out.println("postfix: " + postfix);
		int value = evalPostfix(postfix);
		System.out.println("value: " + value);
	}
}