N,Q = list(map(int,input().split()))
dat = [0] * (N+2)
for i in range(Q):
    l,r = list(map(int,input().split()))
    dat[l] += 1
    dat[r+1] -= 1
count = 0
for i in range(1,N+1):
    dat[i] += dat[i-1]
    if dat[i] % 2 == 1:count += 1
print(count)