//Variable declaration
e=1.6*10**-19;   //charge of electron(c)
epsilon0=8.85*10**-12;    //permittivity(C/Nm)
r0=0.281*10**-9;     //seperation(m)
IE=5.14;     //ionisation energy of Na(eV)
Ea=-3.61;     //electron affinity(eV)

//Calculation
V=-e**2/(4*e*%pi*epsilon0*r0);     
CE=IE+Ea+(V);       //cohesive energy(eV)

//Result
printf('cohesive energy is %0.3f   eV  \n',CE)