L, M = map(int, input().split())
diff = [0] * (L + 2)
for _ in range(M):
    left, right = map(int, input().split())
    diff[left] += 1; diff[right + 1] -= 1
 
s = 0
for i in range(0, L + 1):
    s += diff[i]
    if s > 0:
        L -= 1
print(L + 1)