#!/usr/bin/python3

from collections import defaultdict
from math import log

n = int(input())
bysize = defaultdict(list)
for _i in range(n):
    size, teeth = map(int, input().split())
    bysize[size].append(teeth)

answer = 0
for size, gears in bysize.items():
    n = len(gears)
    if n > 1:
        gears.sort()
        answer += sum(map(log, gears[-(n//2):]))
        answer -= sum(map(log, gears[:n//2]))

print (answer)