Numeric (arithmetic) expressions are formed with numeric operands
  and numeric operators, and yield a single numeric value.

  The term numeric includes logical data, because logical data is
  treated as integer data when used in a numeric context.  (.TRUE.
  is -1; .FALSE.  is 0.)

  The numeric operators are as follows:

       Operator    Description
       -----------------------
          **       exponentiation (evaluated
                            right to left)
          *        multiplication
          /        division
          +        addition
          -        subtraction

  You can use parentheses to force an order of evaluation.