Finally I've found my bug...
Be careful while doing binary search. My problem was that I couldn't find right bounds for it. Then I wrote:
l = 0;
r = 4000000000;

and in the function, which returns possibilit of such element I did such thing:
vl -= 2000000000;
I think, it'll be helpful for someone!

Edited by author 17.11.2007 01:46

i don't use binary search.
i did it with maths, and DP.
but i've WA#11, pls help,
here is my code!!!
   var
   min, i, j, n, fi, fj, fn, x, y, x1, y1 : int64;
   k : integer;

begin
   read(i, fi, j, fj, n);
   min := i;
   if min > j then
     begin
       i := j;
       j := min;
       min := fi;
       fi := fj;
       fj := min;
     end;
     if n < i then
       begin
         x := 1;    y := 0;
         for k := 1 to i-n do
           begin
             min := x;
             inc(x, y);
             y := min;
           end;
         x1 := 1;   y1 := 1;
         for k := 1 to j-n do
           begin
             min := x;
             inc(x1, y1);
             y1 := min;
           end;
         fn := TRUNC((fj*y-fi*y1)/(x1*y+x*y1));
       end
     else
       begin
         x := 1;    y := 0;
         for k := 1 to n-i do
           begin
             min := x;
             inc(x, y);
             y := min;
           end;
         x1 := 1;   y1 := 0;
         for k := 1 to j-i do
           begin
             min := x1;
             inc(x1, y1);
             y1 := min;
           end;
         fn := TRUNC(((fj-x1*fi)*y)/y1+x*fi);
       end;
   writeLn(fn);
end.
if you know my mistake, pls help me!!!
thanks a lot