N, Q = map(int, input().split())
LR = [list(map(int, input().split())) for _ in range(Q)]
la = [0] * N
for l, r in LR:
    la[l - 1] += 1
    la[r - 1] -= 1
    
ans = [0] * (N + 1)
for i in range(N):
    ans[i + 1] = la[i] + ans[i]
    
print(sum(i % 2 == 1 for i in ans))