谁能帮我看看这段tp那里出错了

拜托

program work06;
var n,y,r:integer;
begin
write('please input the year');readln(n);
write('please input the month');readln(y);
case r of
  1,3,5,7,8,10,12: r:=31;
  4,6,9,11: r:=30;
  2:begin
     if (n mod 4=0) then begin
       if (n mod 100=0)then
         begin
           if (n mod 400=0)then
              begin
                r:=29;
              end
           else
              begin
                r:=28;
              end;
         end
       else
         begin
           r:=29;
         end;
      end
     else begin
           r:=28;
          end;
   else writeln('WRONG!');
  end;
writeln('there are',r,'days in this month');
readln;
end.
改过了，可是还是提示“error in statement”