Page calculator

let pages = gets().split(', ');
let itemsPerArr = +gets();
let searchedPage = gets();
let arrOfPageArrays = [];
let notFound = true;

for (let i = 0; i < pages.length; i = i + itemsPerArr) {

    arrOfPageArrays.push(pages.slice(i, i + itemsPerArr))
}

for (let i = arrOfPageArrays.length - 1; i >= 0; i--) {
    if (arrOfPageArrays[i].includes(searchedPage)) {
        print(i + 1);
        notFound = false;
        break;
    }
}

if (notFound) {
    print(-1)
}