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Problem
Read from standard input an **arithmetic expression in postfix notation** (reverse Polish notation), made up of natural numbers and the operators `+`, `-`, `*`, `/`. Tokens (numbers and operators) are separated by single spaces.
Compute the value of the expression using a **stack of numbers** implemented on an array with index `top`. The algorithm is:
- when you encounter a number, push it onto the stack;
- when you encounter an operator, pop two values from the stack (`b` then `a`), compute `a op b`, and push the result back onto the stack.
At the end, exactly one value remains on the stack: the result.
Do not use STL containers.
Input format
Input
input.txt
A single line contains the postfix expression, with tokens separated by spaces. - the expression has at most `5000` characters; - all intermediate numbers and the final result fit in `long long`; - division is integer division between strictly positive numbers; - the expression is always valid (no error checking is required).
Output format
Output
output.txt
The program prints to standard output the value of the expression, followed by a newline.
Example
input
3 4 + 2 *
output
14
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Sample cases (from the problem)
Sample Case 1
Input
3 4 + 2 *
Expected output
14
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