program yukicoder_2399
  use, intrinsic :: iso_fortran_env
  implicit none
  character(len=10) :: s, t
  integer(int32) :: n
  read(input_unit, *) s
  read(input_unit, *) t
  read(input_unit, *) n
  write(output_unit, '(a)') trim(s) // repeat("_"//trim(t), n)
end program yukicoder_2399