a^3 + b^3 + c^ 3 + 3abc > ab(a+b) + bc(b+c) + ac(a+c)

Prove that for all the positive numbers a,b,c the following inequality is valid:

a^3 + b^3 + c^ 3 + 3abc > ab(a+b) + bc(b+c) + ac(a+c)