let I() = stdin.ReadLine()
let N = int(I())
let m n = n % 1000000007L
let f _ =
    let a = I().Split(' ')
    let c,D = int64(a.[0]),m(int64(a.[1]))
    let C = m((c+1L)/2L)
    m(C*D)
seq [1..N] |> Seq.map f |> Seq.fold (fun a b -> m(a+b)) (0L)
|> printfn "%d"