fn main() {
    1       // stack: [1] 
    2       // stack: [1 2]
    3       // stack: [1 2 3]
    4       // stack: [1 2 3 4]
    5       // stack: [1 2 3 4 5]
    println // stack: [1 2 3 4]     prints 5
    println // stack: [1 2 3]       prints 4
    println // stack: [1 2]         prints 3
    println // stack: [1]           prints 2
    println // stack: []            prints 1
}