Evaluating Postfix Expressions -- Example

evaluate: 1 2 3 + 4 * + 5 +                 stack -->
---------------------------                 ---------
push(1)                                     1
push(2)                                     1 2
push(3)                                     1 2 3
pop(), pop(), push(2 + 3)                   1 5
push(4)                                     1 5 4
pop(), pop(), push(5 * 4)                   1 20
pop(), pop(), push(1 + 20)                  21
push(5)                                     21 5
pop(), pop(), push(21 + 5)                  26