var
 a,b,n,i,j:longint;
 c:array[1..100000]of longint;

 function gcd(a,b:longint):longint;
  var r:longint;
  begin
   r:=a mod b;
   while r<>0 do
    begin
     a:=b;b:=r;
     r:=a mod b ;
    end;
   exit(b);
  end;

begin
assign(input,'seq.in');reset(input);
assign(output,'seq.out');rewrite(output);
 readln(n,a,b);
 j:=gcd(a,b);
 for i:=1 to n do
  begin
   read(c[i]);
   if (c[i] mod j)<>0 then
    begin writeln(-1);close(input);close(output);halt; end;
  end;
 randomize;
 writeln((random(4)+1)*n);
close(input);close(output);
end.