4. Bus

passengersInStart = int(input())
stops = int(input())
leftPassengers = passengersInStart

for i in range (1,stops+1):
    s = int(input())
    k = int(input())

    if i % 2 == 1:
        leftPassengers = leftPassengers - s
        leftPassengers = leftPassengers + k + 2
    else:
        leftPassengers = leftPassengers - s - 2
        leftPassengers = leftPassengers + k

print("The final number of passengers is : %d" % leftPassengers)