Bus

function solve (input) {
    let passengersCount = input[0];
    let stopsCount = input[1];
    let stopNumber = 1;

    for (let index = 2; index <= stopsCount * 2; index += 2) {
        passengersCount -= Number(input[index]);
        passengersCount += Number(input[index + 1]);

        if (stopNumber % 2 === 0) {
            passengersCount -= 2;
        } else {
            passengersCount += 2;
        }

        stopNumber++;
    }

    console.log('The final number of passengers is : ' + passengersCount);
}