# Coulomb interatomic energy
import math
#Variable declaration
R=2.81*10**-10 # distance between oppositely charged ion
e=1.6*10**-19 # Charge of an electron
eps=8.854*10**-12 # epsilon
#calculation
U=-(e**2)/(4*math.pi*eps*R)
#Result
print('The Coulomb interatomic energy is %.2f eV'%(U*10**19/1.6))