passengers_number=int(input())
stops_number=int(input())

for i in range (0, stops_number,2):
    passengers_get_off=int(input())
    passengers_get_on=int(input())
    passengers_number=passengers_number-passengers_get_off+passengers_get_on+2
for i in range (1, stops_number, 2):
    passengers_get_off = int(input())
    passengers_get_on = int(input())
    passengers_number=passengers_number-passengers_get_off+passengers_get_on-2


print(f"The final number of passengers is : {passengers_number}")