num = int(input())
if num == 1:
    print(1)
else:
    num -= 1
    ab = 10
    l =1
    n = 2
    while num > 0:
        if num > l:
            num -= l
            n += 1
            t = n ** 2
            while ab < t:
                ab *= 10
                l += 1
        else:
            res = 0
            t = n ** 2
            for i in range(l - num + 1):
                res = t % 10
                t //= 10
            break
    print(res)