from heapq import heappop, heappush
from collections import Counter


def readint():
    return map(int, input().split())


def readlist():
    return list(readint())


n = int(input())
mul4 = 0
mul2 = 0
ans = 0
for _ in range(n):
    k, v = readint()
    if k % 8 == 0:
        ans += v
    elif k % 4 == 0:
        mul4 += v
    elif k % 2 == 0:
        mul2 += v
m = min(mul2, mul4)
ans += m
mul2 -= m
mul4 -= m
ans += mul2 // 3
ans += mul4 // 2
print(ans)