var left1 = document.getElementById('left1');
var right1 = document.getElementById('right1');
var left2 = document.getElementById('left2');
var right2 = document.getElementById('right2');
var left3 = document.getElementById('left3');
var right3 = document.getElementById('right3');
var left4 = document.getElementById('left4');
var right4 = document.getElementById('right4');