function check(a=[7,2,3,2]){
        // table
        val = {}
        val['2']=[2,4,8,6]
        val['3']=[3,9,7,1]
        val['4']=[4,6,4,6]
        val['7']=[7,9,3,1]
        val['8']=[8,4,2,6]
        val['9']=[9,1,9,1]
        simple_ans = [0,1,5,6]

        base = a[0] % 10

        if (a[1]===0) return 1
        if (a[1]===1) return base
        if (simple_ans.indexOf(base) >= 0) return base

        p = a.slice(1) // [2,3,4] => pow(2, pow(3, pow(4,1)))
        console.log(p)
        pv=p.reverse().reduce((acc,v)=>{
                const r=Math.pow(v,acc);
                console.log(`${r}=${v}^${acc}`)
                return r
        },1)
        console.log(pv)

        index4 = (pv % 4)-1
        return val[''+base][index4]
}