Letters

Write down every string of uppercase letters in this order. First the strings of length 1: A, B, …, Z. Then the strings of length 2: AA, AB, …, AZ, BA, BB, …, ZZ. Then the strings of length 3, and so on, with the length growing by one forever. Strings of the same length are listed in lexicographic order.

Concatenating that list from the start gives one endless sequence of uppercase letters. Number the letters of the sequence starting at 0 for the first one. Given an index, find the letter at that position.

The first line contains the index $i$ of a letter. ($0 \le i \le 2 \times 10^9$)

Print the single uppercase letter at position $i$ of the sequence.