N = int(input())
AB = [list(map(int, input().split())) for _ in range(N)]

C = [0]*3
for A, B in AB:
    cnt = 0
    while cnt < 3 and A%2 == 0:
        A //= 2
        cnt += 1
    if cnt:
        C[cnt-1] += B

ans = C[2]
MIN = min(C[:2])
ans += MIN
C[0] -= MIN
C[1] -= MIN
if C[0]:
    ans += C[0]//3
elif C[1]:
    ans += C[1]//2

print(ans)