let MOD = pown 10 9 |> (+)7 |> int64
let R() = stdin.ReadLine()

let solve cs ds =
    let rec f score cs ds =
        match cs, ds with
        | [], _ | _, [] -> score
        | c::cs, d::ds  ->
            let c' = ((c + 1L) / 2L) % MOD
            let d' = d % MOD
            let score' = (c' * d') % MOD
            let newScore = (score + score') % MOD 
            f newScore cs ds             
    f 0L cs ds
    
let N = R() |> int
let C, D =
    let t = List.init N (fun _ -> let t = R().Split() in t.[0], t.[1])
    let c = t |> List.map (fst>>int64)
    let d = t |> List.map (snd>>int64)
    c, d
       
solve C D
|> stdout.WriteLine