function update() {
    don = 0;
    if (document.dons.montant[4].checked) {       
       don = Math.abs(document.dons.autreMontant.value); 
    } else {
       document.dons.autreMontant.value = "";       
       for (i = 0; i<document.dons.montant.length-1; i++) {
          if (document.dons.montant[i].checked) {
            don =  Math.abs(document.dons.montant[i].value);
          }      
       }
    }                 
    // mettre à jour la somme defiscalisée
    don = parseInt(don);
    if (isNaN(don)) don = 0;     
    don_defisc = Math.abs(Math.floor((don*66)/100));   
    //document.dons.montant_defiscalise.value = don_defisc;
}