#! /usr/bin/env python
"""
 massform.py is program which calculates nuclaer binding energy 
 and the nuclear bnding energy per nucleon using the semi-empirical 
 mass formula

 B = a_1*A - a_2*A**(2/3) - a_3*Z**2/a**(1/3) - a_4*(A-2*Z)**2/A 
     + a_5/A**(1/2)

 The program asks the user to input values for the atomic mass number A 
 and the atomic number Z and print out the binding enegry and the binding 
 energy per nucleon

 ### OUTPUT ###
 hpc-login-24 542% massform.py
 Enter atomic number Z: 28
 Enter atomic mass number A: 58
 Binding energy is 493.94 MeV and binding energy per nucleon is 8.52 MeV.

 ###
 Paul Eugenio 
 PHZ4151C
 Jan 15, 2019
"""
# program header code
from __future__ import division, print_function
from math import pi

# define semi-empirical mass formula constanst (MeV)
a1 = 15.67
a2 = 17.23
a3 = 0.75
a4 = 93.2

Z = float(raw_input("Enter atomic number Z: "))
A = float(raw_input("Enter atomic mass number A: "))

# determine constant a5 
if A%2 == 1:   
    a5 = 0         # A is odd
elif Z%2 == 0:
    a5 = 12.0      # A & Z are even
else:
    a5 = -12.0     # A is even and Z is odd

#Calculate binding energy
B = a1*A - a2*A**(2/3) - a3*Z**2/A**(1/3) - a4*(A-2*Z)**2/A + a5/A**(1/2)


print("Binding energy is {0:2d} MeV and binding energy per nucleon is {1:2d} MeV.".format(B, B/A) )