Bus

number_of_people = int(input())
steps = int(input())
counter = 1
people_in = 0
people_out = 0
total_people_bus = 0

while counter <= steps:
    people_out = int(input())
    people_in = int(input())
    if counter % 2 != 0:
        people_bus = number_of_people + people_in + 2 - people_out
    else:
        people_bus = number_of_people + people_in - 2 - people_out
    counter += 1
    number_of_people = people_bus
print(f"The final number of passengers is : {number_of_people}")