13904

n = input()
n = int(n)

arr = []
todo = []

for i in range(1001):
  todo.append(0)

for i in range(n):
  d, w = map(int, input().split())
  arr.append([d,w])
  
arr.sort(key = lambda x:x[1], reverse = True)

i = 0
while True:
  if i == n:
    break
  
  q = arr[i][0]
  while q > 0:
    if todo[q] == 0:
      todo[q] = arr[i][1]
      break
    else:
      q -= 1

  i += 1
  
print(sum(todo))