PROGRAM ex5_7 
IMPLICIT NONE 
REAL :: a= 0, b, x, d = 1.0E-5
DO 
PRINT *, 'Input a positive real number: ' 
READ *, b
IF ( b > 0.0E0 ) EXIT 
END DO 
x = (a+b)/2

DO WHILE (  ABS(x**2)> d  )
PRINT *, '途中のx=',x
x=(x+a)/2
END DO 
PRINT '( 1X, E12.5 )', x 
END PROGRAM ex5_7