#include <bits/stdc++.h>
using namespace std;
inline int Min(int &a, int b) { return a > b ? a = b : a; }
inline int Max(int &a, int b) { return a < b ? a = b : a; }
inline int min(int a, int b) { return a > b ? b : a; }
inline int max(int a, int b) { return a < b ? b : a; }
inline int abs(int a) { return a > 0 ? a : -a; }
const int INF = 1 << 29;
const int mod = 1e9 + 7, N = 500000;
int fac[N], rev[N];
int Pow(int a, int b) {
  int res = 1;
  for (b; b; b >>= 1, a = a * 1ll * a % mod)
    if (b & 1) res = res * 1ll * a % mod;
  return res;
}
int C(int n, int m) {
  if (m > n) return 0;
  int res;
  res = 1ll * fac[n] * rev[m] % mod * rev[n - m] % mod;
  return res;
}
int a, b, k, t;
int main() {
  fac[0] = 1;
  for (int i = 1; i < N; i++) fac[i] = 1LL * fac[i - 1] * i % mod;
  rev[N - 1] = Pow(fac[N - 1], mod - 2);
  rev[0] = 1;
  for (int i = N - 2; i; i--) rev[i] = rev[i + 1] * (i + 1ll) % mod;
  scanf("%d%d%d%d", &a, &b, &k, &t);
  int ans = 0;
  for (int j = 0; j <= 2 * t; j++)
    ans = (ans +
           1ll * Pow(-1, j) * C(2 * t, j) % mod *
               (1ll * C(210000 + 2 * k * t - a + b + 2 * t - 1 -
                            (2 * k + 1) * j + 1,
                        2 * t) -
                C(1 + 2 * k * t - a + b + 2 * t - 1 - (2 * k + 1) * j, 2 * t)) %
               mod) %
          mod;
  ans = (ans % mod + mod) % mod;
  printf("%d\n", ans);
  return 0;
}
