l,m = input().split() a = [input() for _ in range(int(m))] b = [1]*(int(l)+1) # print(len(b)) for i in range(int(m)): for j in range(int(a[i].split()[0]),int(a[i].split()[1])+1): b[j]=0 count = 0 for c in range(len(b)): if b[c]==1: count+=1 print(count)