function solve(n) {
    if (n % 2) return 0;
    let i_max = Math.floor(Math.log2(n));
    let res = 0;
    for (let i = 0; i <= i_max; i++) {
        res += [6, 2, 4, 8][(2 ** i + 2 * n) % 4];
    }
    return res%10; 
}