problem-3.js

function calculateAiCost(tokensUsed) {
    // input gulo number/negative kina check korlam, jodi na hoy tahole Invalid return korbe
    if (typeof tokensUsed !== "number" || tokensUsed < 0) {
        return "Invalid";
    }

    // jodi 500 token ba tar kom use hoy tahole kono taka dite hobe na
    if (tokensUsed <= 500) {
        return 0;
    }

    // notun ekta variable set korlam free 500 token bad diye remaining token ber korar jonno
    let extraTokens = tokensUsed - 500;

    // notun arekta variable set korlam remaining token theke koyta complete 100 token ache seta ber korar jonno
    let chargeableTokens = Math.floor(extraTokens / 100);

    // notun arekta variable set korlam chargeable token diye mot khoroch ber korar jonno
    let totalCost = chargeableTokens * 5;

    return totalCost;

}