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))