Bisection method with while loop

bisection.f

program bisection
  REAL a, b, c, TOL
  INTEGER NMAX, N

  WRITE(*, *) "Enter a and b"
  READ(*, *) a, b

  NMAX = 20
  N = 1
  TOL = 1.0e-04

  do while ( N .lt. NMAX )
    c = (a + b)/2
    PRINT *, "N = ", N, " c = ", c
    if ((b-a)/2 .lt. TOL) then
      ! ROOT FOUND = c
      goto 2
    endif

    N = N + 1
    if ((f(c) .lt. 0) .eqv. (f(a) .lt. 0)) then ! new interval
      a = c
    else
      b = c
    endif
  enddo

1 PRINT *, "OUT OF ITERATION"
2 PRINT *, "RESULT = ", c

end program bisection

REAL function f(x)
  REAL x
  f = x*x*x - x - 2
end function