function extension(){
						var i=1;
						while(i<5){
							var arch = document.getElementById("adj"+i).value;
							var num = arch.length;
							var x = arch.lastIndexOf('.');
							var ext = arch.substring(x,num);
							//alert(ext);
							if((ext!='.jpg')&&(ext!='.gif')&&(ext!= '.bmp')&&(ext!='')){
								document.getElementById("adj"+i).value = ''
								alert("Las extensiones validas son JPG, BMP, GIF")
							}
						i++;
						}
					}