Вот код который я написал, почему он выводит NaN? Как это исправить?

var experiments = Number.isInteger(prompt("Please enter the number of experiments conducted this year: "));
var cat = Number.isInteger(prompt("Please enter the number of experiments conducted on cats: "));
var rat = Number.isInteger(prompt("Please enter the number of experiments conducted on rats: "));
var frog = Number.isInteger(prompt("Please enter the number of experiments conducted on frogs: "));
 
animals = cat + rat + frog;
 
var catResult = cat / experiments * 100;
var ratResult = rat / experiments * 100;
var frogResult = frog / experiments * 100;
 
if (animals > experiments) {
    confirm("You have not conducted so many experiments, there are too many animals indicated!");
} else if (animals < experiments) {
    confirm("You have conducted more experiments, apparently you forgot about someone, check, the number of animals should coincide with the number of experiments!");
} else {
    confirm(`Experiments on cats amounted to: ${catResult}`);
    confirm(`Experiments on rats amounted to: ${ratResult}`);
    confirm(`Experiments on frogs amounted to: ${frogResult}`);
}

<script>
    var experiments = +(prompt("Please enter the number of experiments conducted this year: "));
    var cat = +(prompt("Please enter the number of experiments conducted on cats: "));
    var rat = +(prompt("Please enter the number of experiments conducted on rats: "));
    var frog = +(prompt("Please enter the number of experiments conducted on frogs: "));
             
    animals = cat + rat + frog;
             
    var catResult = cat / experiments * 100;
    var ratResult = rat / experiments * 100;
    var frogResult = frog / experiments * 100;
             
    if (animals > experiments) {
        confirm("You have not conducted so many experiments, there are too many animals indicated!");
    } else if (animals < experiments) {
        confirm("You have conducted more experiments, apparently you forgot about someone, check, the number of animals should coincide with the number of experiments!");
    } else {
        confirm(`Experiments on cats amounted to: ${catResult}`);
        confirm(`Experiments on rats amounted to: ${ratResult}`);
        confirm(`Experiments on frogs amounted to: ${frogResult}`);
    }
</script>