let n, s, k = stdin.ReadLine().Split() |> Array.map int |> fun x -> x.[0], x.[1], x.[2]

let solve s =
  let p = 1_000_000_007L
  // dp[i, j] = i 人目までで合計 j 円になる方法の数
  let dp = Array2D.create (n + 1) (s + 1) 0L in dp.[0, 0] <- 1L
  [1 .. n] |> List.iter (fun i ->
    let a = i * k
    [0 .. s] |> List.iter (fun j ->
      dp.[i, j] <- (dp.[i, j] + dp.[i - 1, j]) % p
      if j >= a then
        dp.[i, j] <- (dp.[i, j] + dp.[i, j - a]) % p
    )
  )
  dp.[n, s]

let minTotal = (n - 1) * n / 2 * k
solve (max 0 (s - minTotal))
|> stdout.WriteLine