class List {
    constructor() {
        this.list = null
    }

    push(v) {
        if (this.list == null) {
            this.list = () => {
                this.list = null
                return v
            }
        } else {
            let temp = this.list

            this.list = () => {
                this.list = temp

                return v
            }
        }
    }

    pop() {
        if (this.list == null) {
            throw new Error('empty')
        }

        return this.list()
    }

    length() {
        let count = 0
        let temp = new List()

        while (this.list != null) {
            temp.push(this.pop())

            count++
        }

        while (temp.list != null) {
            this.push(temp.pop())
        }

        return count
    }

    nth(n) {
        let temp = new List()
        let len = this.length()
        let idx = len - n

        while (idx > 1) {
            idx--

            temp.push(this.pop())
        }

        let retVal = this.pop()
        temp.push(retVal)


        idx = len - n


        while (idx > 0) {
            idx--

            this.push(temp.pop())
        }

        return retVal
    }
}

let l = new List()

l.push('hello')
l.push(10)
l.push(20)
l.push(30)
l.push('bye')

console.log(l.length())

console.log(l.nth(1))

console.log(l.pop())
console.log(l.pop())
console.log(l.pop())
console.log(l.pop())
console.log(l.pop())