function bus(input) {

    let passengersCnt = Number(input.shift());  //брой пътници
    let stops = Number(input.shift());  //брой спирки

    for (let i = 1; i <= stops; i++) {
        let descending = Number(input.shift());  //слизащи
        let gettingOn = Number(input.shift());   //качващи се

        if (i % 2 === 1) {
            passengersCnt = passengersCnt + gettingOn + 2 - descending;

        } else {
            passengersCnt = passengersCnt + gettingOn - 2 - descending;
        }
    }
    console.log(`The final number of passengers is : ${passengersCnt}`);
}