Задание 1

! Вариант 3/93 в Шелесте



program hello
    implicit none
    integer :: n
    real(8) :: fact
    do while (.true.)
        write (*,'(1x,a$)') 'Enter n:'
        read (*,*) n
        if (n >= 20 .or. n <0 ) then
            write (*,*) 'Incorrect enter!'
            cycle
        else
            exit
        end if
    end do
    !write (*,*) 'Factorial n:', fact(n)
    write (*,'(1x,a f20.5)') 'Factorial n:', fact(n)
end program
real(8) function fact(r)
    real(8), parameter :: pi = 3.141592653589793, e = 2.718281828459045
    real(8):: ratio(5)
    real :: multi_1, multi_2
    integer :: r,i
    ratio = [1.0, (1.0/12.0), (1.0/288.0), (-139.0/51480.0), (-571.0/2488320.0)]
    !
    fact = 0.000000
    if (r == 0) then
        fact = 1.00000000
    else
        do i = 1, size(ratio)
            fact = fact + ratio(i)/(r**(i-1))
        end do
        fact = fact*sqrt(2*pi*r)*( (r/e)**r )
    end if
    !multi_2 = ratio_1 + (ratio_2/r) + (ratio_3/(r**2)) + (ratio_4/(r**3)) + (ratio_5/(r**4))
    !fact = multi_1*multi_2
end function