from collections import Counter


def count_f2(n: int) -> int:
    cnt = 0
    x = n
    while x > 0 and x % 2 == 0:
        cnt += 1
        x //= 2

    return cnt


N = int(input())
freq = Counter()
ans = 0
for _ in range(N):
    A, B = map(int, input().split())
    match count_f2(A):
        case 1:
            freq[1] += B
        case 2:
            freq[2] += B
        case x if x > 2:
            ans += B

x = min(freq[1], freq[2])
ans += x
ans += (freq[1] - x) // 3
ans += (freq[2] - x) // 2
print(ans)