SPOJ PIR

use the formula for volume of irregular tetrahedral of given sides. first pair the given sides such that they don't have any common vertices. and name it (u,U),(v,V), (w,W) Volume = sqrt(4*u*u*v*v*w*w- u*u*sqr((v*v+w*w - U*U)) - v*v*sqr((w*w+u*u - V*V)) - 			w*w*sqr((u*u + v*v - W*W)) + (v*v +w*w - U*U)*(w*w+u*u- V*V)*(u*u+v*v - W*W))/12;

Reference: http://www.cs.berkeley.edu/~wkahan/VtetLang.pdf