So the surface integral of R times k dot n, the dot product of k and n, ds can be rewritten as the-- let me write it this way-- can be rewritten as the surface integral over S2 of R times k dot n ds, plus the surface integral-- I'm just breaking up the surface here-- plus the surface integral over S1 of R times k dot n ds plus the surface integral over surface three of the same thing, R times k dot n ds. 