n,m = input().split() n = int(n) m = int(m) # m=8 工程队 a = [ 1 for x in range(n+1)] #a[0] ,a[1] …… a[n] for i in range(m): b,c = input().split() #a起点，b终点 b,c = int(b),int(c) for j in range(b,c+1): a[j] = 0 #把原来的1变成0 ，表示这颗树砍掉 s = 0 for x in range(n+1): if a[x]==1: s= s + 1 print(s) """ Input 500 3 150 300 100 200 470 471 Output 298 """