ab = input().split() a = int(ab[0]) b = int(ab[1]) s = [] for i in range(0,a+1): s.append(str(i)) for k in range(b): cd = input().split() c = int(cd[0]) d = int(cd[1]) for y in range(c,d+1): if str(y) in s: s.remove(str(y)) print(len(s))