N = int(input())
A = list()
B = list()
cnt8 = 0
cnt4 = 0
cnt2 = 0
for _ in range(N):
    a,b = map(int, input().split())
    if a%8==0:
        cnt8 += b
    elif a%4==0:
        cnt4 += b
    elif a%2==0:
        cnt2 += b
    else:
        continue
ans = cnt8
minn = min(cnt4,cnt2)
ans += minn
cnt4 -= minn
cnt2 -= minn
ans += cnt4//2
ans += cnt2//3
print(ans)