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## Problem Description
From beginning till end, this message has been waiting to be conveyed.
For a given unordered multiset of n lowercase English letters ("multi" means that a letter may appear more than once), we treat all letters as strings of length 1, and repeat the following operation n - 1 times:
* Remove any two elements s and t from the set, and add their concatenation s + t to the set.
The cost of such operation is defined to be <image>, where f(s, c) denotes the number of times character c appears in string s.
Given a non-negative integer k, construct any valid non-empty set of no more than 100 000 letters, such that the minimum accumulative cost of the whole process is exactly k. It can be shown that a solution always exists.
Input
The first and only line of input contains a non-negative integer k (0 ≤ k ≤ 100 000) — the required minimum cost.
Output
Output a non-empty string of no more than 100 000 lowercase English letters — any multiset satisfying the requirements, concatenated to be a string.
Note that the printed string doesn't need to be the final concatenated string. It only needs to represent an unordered multiset of letters.
Examples
Input
12
Output
abababab
Input
3
Output
codeforces
Note
For the multiset {'a', 'b', 'a', 'b', 'a', 'b', 'a', 'b'}, one of the ways to complete the process is as follows:
* {"ab", "a", "b", "a", "b", "a", "b"}, with a cost of 0;
* {"aba", "b", "a", "b", "a", "b"}, with a cost of 1;
* {"abab", "a", "b", "a", "b"}, with a cost of 1;
* {"abab", "ab", "a", "b"}, with a cost of 0;
* {"abab", "aba", "b"}, with a cost of 1;
* {"abab", "abab"}, with a cost of 1;
* {"abababab"}, with a cost of 8.
The total cost is 12, and it can be proved to be the minimum cost of the process.
## Contest Information
- **Contest ID**: 849
- **Problem Index**: C
- **Points**: 500.0
- **Rating**: 1600
- **Tags**: constructive algorithms
- **Time Limit**: {'seconds': 1, 'nanos': 0} seconds
- **Memory Limit**: 256000000 bytes
## Task
Solve this competitive programming problem. Provide a complete solution that handles all the given constraints and edge cases. |