program montecarlo 


real :: randomNumber,error,area,deltaArea
real :: xRandom,yRandom
integer :: totalPoints, areaPoints



 call initRandomSeed();
error = 0.01
deltaArea  = 1.0

arePoints = 0
totalPoints = 0

do while (deltaArea > error)

   call random_number(randomNumber)
   xRandom = randomNumber
   call random_number(randomNumber)
   yRandom = randomNumber

   if (yRandom < cos(xRandom)) then
      areaPoints = areaPoints + 1
   end if
  
   totalPoints = totalPoints + 1
   area = areaPoints*1.0/totalPoints
   print*, area
   deltaArea = abs( area - areaOld)
   areaOld = area

end do

!---------------------------------------------------------
contains

subroutine initRandomSeed()

   integer :: i, n, clock
   integer, dimension(:), allocatable :: seed
   
   call random_seed(size = n)
   allocate(seed(n))
   call system_clock(count=clock)
   seed = clock + 37 * (/ (i - 1, i = 1, n) /)
   call random_seed(put = seed)
   deallocate(seed)
   
end subroutine initRandomSeed

end program montecarlo