import string
import sys
from itertools import count


def input(): return sys.stdin.readline().rstrip('\n')


def main():
    n = int(input())
    for l in count(1):
        if n < 26 ** l:
            ans = ''
            for _ in range(l):
                ans = string.ascii_uppercase[n % 26] + ans
                n //= 26
            print(ans)
            return

        else:
            n -= 26 ** l


if __name__ == '__main__':
    main()