program abc171
    use,intrinsic :: iso_fortran_env
    implicit none
    integer(int64):: n, ni, val
    character(20):: ans
    
    read*, n
    ans = ''
    do while(n>0)
        ni = mod(n-1,26_8)
        val = ni + ichar('a')
        ans = char(val) //trim( ans)
        n=n/26
    end do
    print'(a)', ans
end program abc171