N = int(input())
ans = 0

cnt = [0] * 4

for _ in range(N):
    A, B = map(int, input().split())
    v = 0
    while A % 2 == 0:
        A //= 2
        v += 1

    cnt[min(v, 3)] += B

ans = cnt[3]
ans += min(cnt[1], cnt[2])

if cnt[1] > cnt[2]:
    ans += (cnt[1] - cnt[2]) // 3
else:
    ans += (cnt[2] - cnt[1]) // 2

print(ans)