Euler002

program euler002
    implicit none
    
    integer :: i = 0
    integer :: f = 0
    integer :: s = 0
    
    do
        i = i + 1
        f = fib(i)
        
        if (f >= 4e6) then
            exit
        else if (mod(f,2)==0) then
            s = s + f
        end if
    end do
        
    print *, 'Fibs: ', s
    
    contains
        recursive function fib(n) result (r)
            integer n, r
            
            if (n < 1) then
                r = 0
            else if (n < 3) then
                r = 1
            else
                r = fib(n-1) + fib(n-2)
            end if
            return
        end function fib

end program euler002