!-----  Ex5_7: Square Root   -----
      REAL :: r, x, d = 0.000005
      PRINT*,'Input a real number:'
      READ*, r
      IF(r>0) THEN
             x = r
         DO  WHILE( ABS(x**2 - r) > d )
             x = 0.5*( x + r/x)
         END DO
         PRINT '(F8.5)', x
      END IF
      END