1177B - Digits Sequence (Hard Edition) - CodeForces Solution

import math

n = int(input())
num1 = 0
num = 9
i = 1

while num < n:
    num1 = num
    num = num + 9 * pow(10, i) * (i + 1)
    i += 1
    
power = i - 1
nine = 0
for j in range(power):
    nine = nine * 10 + 1
    
nine *= 9
rem = num1
num1 = math.ceil((n - num1) / (power + 1)) + nine
num1 = str(num1)
rem = (n - rem - 1) % (power + 1)

print(num1[rem])