diff --git a/Fortran/exercise1/calc_pi.f90 b/Fortran/exercise1/calc_pi.f90
index 1833099..022c386 100644
--- a/Fortran/exercise1/calc_pi.f90
+++ b/Fortran/exercise1/calc_pi.f90
@@ -1,10 +1,11 @@
 program calc_pi
+use iso_fortran_env
 implicit none
 
 integer, parameter :: num_samples = 1000000  ! Number of random samples
 
-real :: x, y
-real :: pi_approx
+real(real64) :: x, y
+real(real64) :: pi_approx
 integer :: i, count_inside_circle
 
 count_inside_circle = 0
@@ -14,7 +15,7 @@ program calc_pi
     call random_number(x)
     call random_number(y)
     
-    if (x**2 + x**2 <= 1.0) then
+    if (x**2 + y**2 <= 1.0) then
         count_inside_circle = count_inside_circle + 1
     end if
 end do