bus

<?php

$passengersBeginnig= intval(readline());
$numberBusStops= intval(readline());
$countBusStops=0;
$passengersInBus= $passengersBeginnig;
while($countBusStops<$numberBusStops){
  $countBusStops++;

   $passengersOut= intval(readline());
   $passengersInBus-=$passengersOut;
    $passengersEnter= intval(readline());
     $passengersInBus+=$passengersEnter;
    if($countBusStops%2==1){
   $passengersInBus+=2;

    }
    if($countBusStops%2==0){
    $passengersInBus-=2;

    }
}
echo "The final number of passengers is : $passengersInBus";