n = read_line.to_i
cs = Array.new(4, 0i64)
n.times do
  a, b = read_line.split.map(&.to_i)
  c2 = 0
  while a % 2 == 0 && c2 < 3
    a //= 2
    c2 += 1
  end
  cs[c2] += b
end
c12 = {cs[2], cs[1]}.min
ans = cs[3] + c12
cs[2] -= c12
cs[1] -= c12
ans += cs[2] // 2 + cs[1] // 3
puts ans