advent of code day 1

day1.f90

program day1
  implicit none

  integer :: stat, m, s, s2

  s = 0
  s2 = 0
  open(1, file="day1.in", iostat=stat)
  do
    read(1, *, iostat=stat) m
    if (stat /= 0) exit

    s = s + (m / 3) - 2
    s2 = s2 + launch(m)
  end do
  print *, s, s2

  close(1)
contains
  recursive function launch(m) result(res)
    integer, intent(in) :: m
    integer :: res, x

    x = m/3 - 2
    if (x < 0) then
      res = 0
    else
      res = x + launch(x)
    end if
  end function launch
end program day1