백준 구현 대비 달력

cal=[[0 for i in range(367)] for i in range(1000)]
dict={}
for i in range(2,14):
  dict[i]=0

# 여기에는 놓일 위치
work=[]
n=int(input())
for i in range(n):
  s,e=map(int, input().split())
  work.append([s,e])

work.sort(key=lambda x:(x[0],-x[1]))
for w in work:
  s,e=w[0],w[1]
  count=0
  for j in range(s,e+1):
    while cal[count][j]==1:
      count+=1
  for j in range(s,e+1):
    cal[count][j]=1

answer=0
ga,se=0,0
for j in range(367):
  flag=True
  count=0
  for i in range(1000):
    if cal[i][j]==1:
      flag=False
      count=i
  se=max(count,se)
  if flag:
    answer+=ga*(se+1)
    ga,se=0,0
  else:
    ga+=1


print(answer)