1993*19941994+1994*19931993
=1993*1994*10001+1994*1993*10001
=2*1993*1994*10001
=2*10001*(2000-7)*(2000-6)
=2*10001*(2000*2000-13*2000+42)
=2*10001*(4000000-26000+42)
=2*(10000+1)*3974042
=7948084*(10000+1)
=79480840000+7948084=79488788084