n,m,=input().split() n=int(n) m=int(m) a=[1 for x in range(n+1)] for i in range(m): c,b=input().split() c=int(c) b=int(b) for j in range(c,b+1): a[j]=0 s=0 for x in range(n+1): if a[x]==1: s=s+1 print(s)