function CambiarDias(){
    var cmbDia = document.getElementById("cmbDia");

    cmbDia.length = 0
    var intMes = document.getElementById("cmbMes");

    switch(parseInt(intMes.value)){
        case 1,3,5,7,8,10,12:
            var contar = 31;
            break;
        case 2:
            var contar = 28
            break;
        case 4,6,9,11:
            var contar = 30
            break;
        default:
            var contar = 31;
            break;
    }

    cmbDia.length=contar;

    for(i=0;i<contar;i++){
        var opcion = new Option(i,i)
        cmbDia.options[i].value = i+1
        cmbDia.options[i].text = i+1
    }
}

function DisabledButton(){
    var boton = document.getElementById("btn_enviar");
    boton.disabled = true;
}