def pow2(x):
    cnt = 0
    while x%2==0:
        cnt += 1
        x //= 2
    return cnt
N = int(input())
C = {0:0,1:0,2:0,3:0}
for _ in range(N):
    a,b = map(int,input().split())
    n = pow2(a)
    if n>=3:
        C[3] += b
    else:
        C[n] += b
ans = C[3]
m = min(C[1],C[2])
ans += m
C[1] -= m
C[2] -= m
ans += C[1]//3+C[2]//2
print(ans)