#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:102400000,102400000")
using namespace std;
template <class T, class U>
inline void Max(T &a, U b) {
  if (a < b) a = b;
}
template <class T, class U>
inline void Min(T &a, U b) {
  if (a > b) a = b;
}
inline void add(int &a, int b) {
  a += b;
  while (a >= 1000000007) a -= 1000000007;
}
int pow(int a, int b) {
  int ans = 1;
  while (b) {
    if (b & 1) ans = ans * (long long)a % 1000000007;
    a = (long long)a * a % 1000000007;
    b >>= 1;
  }
  return ans;
}
long long C(int a, int b) {
  long long ans = 1, res = 1;
  for (int i = 1; i < b + 1; i++)
    ans = ans * (a - i + 1) % 1000000007, res = res * i % 1000000007;
  return ans * pow((int)res, 1000000007 - 2) % 1000000007;
}
int main() {
  int i, j, k = 0, ca = 0, m, T, K, n;
  int a, b;
  scanf("%d%d%d%d", &a, &b, &k, &T);
  int s = 2 * k * T + a - b - 1;
  n = 2 * T;
  m = 2 * k + 1;
  long long ans = 0;
  for (int i = 0; i < n; i++) {
    j = s - m * i;
    if (j < 0) break;
    ans += (i & 1 ? -1LL : 1LL) * C(n, i) * C(n + j, n) % 1000000007;
  }
  ans %= 1000000007;
  if (ans < 0) ans += 1000000007;
  printf("%d\n", ans);
  return 0;
}
