Calculadora de EXP

function XPCalc()
{
var XP = 0;
var lvl;
var x;
var CurXP=0;
lvl = window.document.XP.Level.value;
CurXP=window.document.XP.CurXP.value;
x = ((50/3)*Math.pow(lvl,3))-(100*Math.pow(lvl,2))+((850/3)*lvl)-200-CurXP;
x = Math.floor(x);
XP =+x;
window.document.XP.Display.value = XP;

}