X3:=(20*X2+19*REF(X2,1)+18*REF(X2,2)+17*REF(X2,3)+16*REF(X2,4)+15*REF(X2,5)+14*REF(X2,6)+13*REF(X2,7)+12*REF(X2,8)+11*REF(X2,9)+10*REF(X2,10)+9*REF(X2,11)+8*REF(X2,12)+7*REF(X2,13)+6*REF(X2,14)+5*REF(X2,15)+4*REF(X2,16)+3*REF(X2,17)+2*REF(X2,18)+REF(X2,20))/210;