Tourist Shop

function touristShop(input) {
    let i = 0;
    let sum = 0;
    let counter = 0;
    let budget = Number(input[i++]);
    let command = input[i++];

    while (command !== "Stop" && sum <= budget) {
        let price = Number(input[i++]);
        counter++;
        if (counter % 3 === 0) {
            price /= 2;
        }
        sum += price;
        command = input[i++];
    }

    if (command === "Stop") {
        console.log(`You bought ${counter} products for ${sum.toFixed(2)} leva.`);
    } else {
        console.log("You don't have enough money!")
        console.log(`You need ${(sum - budget).toFixed(2)} leva!`)
    }
}

РЕШЕНИЕ СЪС SHIFT():

function touristShop(input) {
    let sum = 0;
    let counter = 0;
    let budget = Number(input.shift());
    let command = input.shift();

    while (command !== "Stop" && sum <= budget) {
        let price = Number(input.shift());
        counter++;
        if (counter % 3 === 0) {
            price /= 2;
        }
        sum += price;
        command = input.shift();
    }

    if (command === "Stop") {
        console.log(`You bought ${counter} products for ${sum.toFixed(2)} leva.`);
    } else {
        console.log("You don't have enough money!")
        console.log(`You need ${(sum - budget).toFixed(2)} leva!`)
    }
}

РЕШЕНИЕ С FOR:

function touristShop(input) {
    let sum = 0;
    let budget = Number(input[0]);

    for (let i = 1; i < input.length; i++) {
        let command = input[i];
        if (command === "Stop") {
            console.log(`You bought ${parseInt(i / 2)} products for ${sum.toFixed(2)} leva.`);
            break;
        }
        let priceProduct = Number(input[++i]);
        if (i % 3 === 0) {
            priceProduct /= 2;
        }
        sum += priceProduct;

        if (sum > budget) {
            console.log("You don't have enough money!");
            console.log(`You need ${(sum - budget).toFixed(2)} leva!`);
            break;
        }
    }
}

И ЛЕКО ТАРИКАТСКАТА СЪС SHIFT() И ТЕРНАРЕН ОПЕРАТОР:

function touristShop(input) {
    let sum = 0;
    let budget = Number(input.shift());

    for (let i = 1; i < Number.MAX_SAFE_INTEGER; i++) {
        if (input.shift() === "Stop") {
            console.log(`You bought ${--i} products for ${sum.toFixed(2)} leva.`);
            break;
        }

        sum += Number(input.shift()) * (i % 3 === 0 ? 0.5 : 1);

        if (sum > budget) {
            console.log(`You don't have enough money!\nYou need ${(sum - budget).toFixed(2)} leva!`);
            break;
        }
    }
}