Three Different Numbers

This is probably the simplest problem ever. You just need to count the number of ordered triples of different numbers (X1, X2, X3), where Xi could be any positive integer from 1 to Ni, inclusive (i = 1, 2, 3). No, wait. I forgot to mention that numbers N1, N2, N3 could be up to 1018. Well, in any case it is still quite simple :) By the way, because of this the answer could be quite large. Hence