function check(wert) {
	if (isNaN(wert)) {
    	return Number(0);
 	} else {
  		return wert;
 	}
}

function summe() {
  var x = 0;
  
  var mengexs = Number(window.document.question.menge_XS.value);
  var menges = Number(window.document.question.menge_S.value);
  var mengem = Number(window.document.question.menge_M.value);
  var mengel = Number(window.document.question.menge_L.value);
  var mengexl = Number(window.document.question.menge_XL.value);
  var mengexxl = Number(window.document.question.menge_XXL.value);
  var mengeother = Number(window.document.question.menge_andere.value);
  
  mengexs = check(mengexs);
  menges = check(menges);
  mengem = check(mengem);
  mengel = check(mengel);
  mengexl = check(mengexl);
  mengexxl = check(mengexxl);
  mengeother = check(mengeother);
  
  x = eval(mengexs + menges + mengem + mengel + mengexl + mengexxl + mengeother);
  window.document.question.gesamt.value = x;
}