N = int(input())
A, B = [0]*N, [0]*N

one, two = 0, 0
ans = 0
for i in range(N):
	A[i], B[i] = map(int, input().split())
	if A[i]%8 == 0:
		ans += B[i]
	elif A[i]%4 == 0:
		two += B[i]
	elif A[i]%2 == 0:
		one += B[i]

if one >= two:
	ans += two + (one - two) // 3
else:
	ans += one + (two - one) // 2
print(ans)