program Tinh_tong_cac_chan;
uses crt;
var a,b,S,i:longint;
BEGIN
clrscr;
S:=0;
write('Cho a = ');readln(a);
write('Cho b = ');readln(b);
if (a<0) or (b<0) then writeln('So da nhap khong hop le!')
else for i:=a to b do
begin
if i mod 2 = 0 then S:=S+i;
writeln('Tong cac so chan tu a den b la : ',S);
end;
readln;
END.