function lastDigit(a, b) {
    if(a == 0 && b != 0)
        return 0;
    if(b == 0 || a == 1)
        return 1;
    if(b == 1)
        return a;

    var sA = ''+a;
    var sB = ''+b;
    console.log("a len is : " +sA.length);
    console.log("b len is : " +sB.length);

    var md4 = b%4;
    var exp = md4 == 0 ? 4 : md4;
    var res = parseInt(sA[sA.length-1])**exp
    //return (a**b)%10
    return res%10
}