#include <bits/stdc++.h>
using namespace std;
const long long K = 1000, T = 100, MXM = K * T + 110,
                MOD = 1000 * 1000 * 1000 + 7;
long long a, b, k, t, ans, dp[2][2 * MXM + 10], cp[2][2 * MXM + 10],
    ps[2][2 * MXM + 10], qs[2][2 * MXM + 10];
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long i, j;
  cin >> a >> b >> k >> t;
  dp[0][MXM + a] = 1;
  cp[0][MXM + b] = 1;
  for (i = MXM + min(a, b); i <= 2 * MXM; ++i) {
    ps[0][i] = ps[0][i - 1] + dp[0][i];
    qs[0][i] = qs[0][i - 1] + cp[0][i];
  }
  for (i = 1; i <= t; ++i)
    for (j = 1; j <= 2 * MXM; ++j) {
      dp[i % 2][j] = (MOD + ps[!(i % 2)][min(2 * MXM, j + k)] -
                      ps[!(i % 2)][max(0LL, j - k - 1)]) %
                     MOD;
      cp[i % 2][j] = (MOD + qs[!(i % 2)][min(2 * MXM, j + k)] -
                      qs[!(i % 2)][max(0LL, j - k - 1)]) %
                     MOD;
      ps[i % 2][j] = (ps[i % 2][j - 1] + dp[i % 2][j]) % MOD;
      qs[i % 2][j] = (qs[i % 2][j - 1] + cp[i % 2][j]) % MOD;
    }
  for (i = 1; i <= 2 * MXM; ++i)
    ans = (ans + ((dp[t % 2][i] * qs[t % 2][i - 1]) % MOD)) % MOD;
  cout << ans << '\n';
  return 0;
}
