program p1e1
  implicit none
  integer*4 :: SEED, i, NRAND
  real*8 :: x, sum1, sum2, sigma, genrand_real2

  SEED = 23456
  NRAND = 50000

  call init_genrand(SEED)

  sum1 = 0.0d0
  sum2 = 0.0d0

  do i = 1, NRAND
    x = genrand_real2()
    write (*, *) i, x
    sum1 = sum1 + x
    sum2 = sum2 + x*x
  enddo

  sum1 = sum1/real(NRAND)
  sum2 = sum2/real(NRAND)
  sigma = dsqrt(sum2 - sum1*sum1)

  write (*, *) sum1, sigma
endprogram p1e1