05. Bus

# 05. Bus

travelers = int(input())
stops = int(input())
i = 1
while i <= stops:
    if i % 2 == 0:
        travelers -= int(input())
        travelers += int(input())
        travelers -= 2
    else:
        travelers -= int(input())
        travelers += int(input())
        travelers += 2
    i += 1
print(f"The final number of passengers is : {travelers}")