Hello, I've been trying to solve this problem 1811E - Living Sequence and i couldnt The problem states that we want to delete all numbers that contain 4 as a digit and then find what is the number is position k . i read the editorial and i have a question,if you didnt solve it and dont wana see solution, ignore this blog. . . . the solution says we want delete one digit the we have to convert number from base 10 to base 9 and then add every digit by one where this digit >= 4. why we add 1 for those digit and if i want delete like 2 digit (6, 7) then i have to convert number from base 10 to base 8 ? and increase every digit >= 6 or >= 7 by one ? i didnt understand i i tried to see some expalin on youtube but no one say why we add one.

thank you very much