An interview with an HR representative was conducted. They were super rude and did not care about the actual candidate.

Following that, a Codility test was administered.

Subsequently, a standard "bye" email was received.

You receive a string with operations as input:

• If it is a number, push it to the stack.
• If it is "DUP", duplicate the top element and push it to the stack.
• If it is "POP", remove the top element.
• If it is "+", add the two numbers on top of the stack and replace both with the result of the addition.
• If it is "-", subtract the two numbers on top (the second minus the first) of the stack and replace both with the result of the subtraction.
• If an error occurs (e.g., not enough numbers to add/subtract/pop), return -1.

Examples:

Input: "3 DUP 5 - -" Output: -1

Input: "13 DUP 4 POP 5 DUP + DUP + -" Output: 7

Input: "5 6 + -" Output: -1