public static int evaluate(String expression) {
		Stack211<Integer> stack = new Stack211<Integer>();
		for (int i = 0; i < expression.length(); i++) {
			char c = expression.charAt(i);
			if (c >= '0' && c <= '9') {
				int num = c - '0';
				stack.push(num);
			} else {
				int val1 = stack.pop();
				int val2 = stack.pop();
				if (c == '+') {
					stack.push(val2 + val1);
				} else if (c == '-') {
					stack.push(val2 - val1);
				} else if (c == '*') {
					stack.push(val2 * val1);
				} else {
					stack.push(val2 / val1);
				}

			}
		}
		return stack.pop();
	}