program main;

var
  x, y: array[0..0] of integer;
  a, b: integer;

function exgcd(a, b: integer; var x, y: integer): integer;
var
  t, r: integer;
begin
  if b = 0 then
  begin
    x := 1;
    y := 0;
    exgcd := a;
  end
  else
  begin
    r := exgcd(b, a mod b, x, y);
    t := x;
    x := y;
    y := (t - (a div b) * y);
    exgcd := r;
  end;
end;


begin
  a := 7;
  b := 15;
  x[0] := 1;
  y[0] := 1;
  exgcd(a, b, x[0], y[0]);
  x[0] := ((x[0] mod b) + b) mod b;
  write(x[0]);
end.