[백준] 1263 파이썬 python

n = int(input())
t = []
for i in range(n):
  t.append(tuple(map(int, input().split()))) 

t.sort(key = lambda x : x[1], reverse=True)
# print(t)
now = t[0][1]
for i in range(n):
  if now > t[i][1]:
    now = t[i][1]
  task = t[i][0]
  now = now - task
  # print(now, t[i][1])
if now < 0:
  print(-1)
else:
  print(now)