var bg= "http://s7.directupload.net/images/130723/kur6kpfc.png";

if(screen.width < 801) bg="http://s1.directupload.net/images/130723/u32w35ih.png";
else if(screen.width < 960) bg="http://s14.directupload.net/images/130723/bjitskdf.png" ;
else if(screen.width < 1025) bg="http://s1.directupload.net/images/130723/jersdeda.png";
else if(screen.width < 1281) bg="http://s7.directupload.net/images/130723/m5e9cvyt.png";
else if(screen.width < 1441) bg="http://s14.directupload.net/images/130723/nmu6oivk.png";
else if(screen.width < 1601) bg="http://s1.directupload.net/images/130723/indrbuu6.png";
else if(screen.width < 1921) bg="http://s7.directupload.net/images/130723/kur6kpfc.png";


document.body.style.backgroundImage="url("+bg+")";