function changeMonth(){
var year = document.getElementById( "year" ).value;
var month = document.getElementById( "month" ).value;
var date = document.getElementById( "date" ).options;
var length=0;
if(month==1){
length=31;
}else if(month==2){
if(year%4==0){
length=29;
}else{
length=28;
}
}else if(month==3){
length=31;
}else if(month==4){
length=30;
}else if(month==5){
length=31;
}else if(month==6){
length=30;
}else if(month==7){
length=31;
}else if(month==8){
length=31;
}else if(month==9){
length=30;
}else if(month==10){
length=31;
}else if(month==11){
length=30;
}else if(month==12){
length=31;
}
date.length=1;
for (i=1;i<=length;i++){
date[i]=new Option(i,i);
}
}
function setDate(value){
var date = document.getElementById( "date" ).options;
var length = date.length;
for (i=1;i<=length;i++){
if(date[i]!=null)
if (date[i].value==value)
date[i].selected=true;
}
}