l,m=map(int,input().split()) ls=[] u=0 l=l+1 for i in range(m): c,d=map(int,input().split()) l=l-(d-c+1) ls.append((c,d)) ls.sort() for i in range(1,m): if ls[i][0]<=ls[i-1][1] : u=u+ls[i-1][1]-ls[i][0]+1 l=l+u print(l)