toI(s=readline()) = parse(Int,s)
toVI(s=readline()) = parse.(Int,split(s))
rep(f,n) = [f() for _ in 1:n]
@enum YN Yes=1 No=0

function main()
    n = toI()
    ab = rep(toVI,n)
    solve(n,ab) |> println
end

function solve(n,ab)
    cnt = zeros(Int,4)
    for (a,b) in ab
        if a % 8 == 0
            cnt[1] += b
        elseif a % 4 == 0
            cnt[2] += b
        elseif a % 2 == 0
            cnt[3] += b
        else
            cnt[4] += b
        end
    end
    res = cnt[1]
    d = min(cnt[2],cnt[3])
    res += d
    cnt[2] -= d; cnt[3] -= d
    res += fld(cnt[2],2) + fld(cnt[3],3)
    res
end

@static if endswith(@__FILE__, PROGRAM_FILE)
    main()
end