l,m = map(int,input().strip().split()) regin = [] for _ in range(m): a,b = map(int,input().strip().split()) regin.append((a,b)) totals = l +1 remove_trees = overlaps = 0 removed = [False] * (l+1) for (a,b) in regin: for i in range(a,b+1): if not removed[i]: remove_trees += 1 removed[i] = True else: overlaps += 1 remain = totals - remove_trees print(remain)