L,M=map(int,input().split()) results=[] for _ in range(M): a,b=map(int,input().split()) results.append((a,b)) trees=[False]*(L+1) for start , end in results: for i in range(start,end+1): trees[i]=True count=0 for i in range(L+1): if not trees[i]: count+=1 print(count)