#include <bits/stdc++.h>   using namespace std;   template <class T>   T extgcd(T a, T b, T& x, T& y) {     for (T u = y = 1, v = x = 0; a;) {       T q = b / a;       swap(x -= q * u, u);       swap(y -= q * v, v);       swap(b -= q * a, a);     }     return b;   }   template <class T>   T mod_inv(T a, T m) {     T x, y;     extgcd(a, m, x, y);     return (m + x % m) % m;   }   long long mod_pow(long long a, long long n, long long mod) {     long long ret = 1;     long long p = a % mod;     while (n) {       if (n & 1) ret = ret * p % mod;       p = p * p % mod;       n >>= 1;     }     return ret;   }   template <long long mod, long long primitive_root>   class NTT {    public:     long long get_mod() const { return mod; }     void _ntt(vector<long long>& a, long long sign) {       const long long n = ((long long)(a).size());       const long long g = primitive_root;       long long h = (long long)mod_pow(g, (mod - 1) / n, mod);       if (sign == -1) h = (long long)mod_inv(h, mod);       long long i = 0;       for (long long j = 1; j < n - 1; ++j) {         for (long long k = n >> 1; k > (i ^= k); k >>= 1)           ;         if (j < i) swap(a[i], a[j]);       }       for (long long m = 1; m < n; m *= 2) {         const long long m2 = 2 * m;         const long long base = mod_pow(h, n / m2, mod);         long long w = 1;         for (long long x = 0; x < (m); x++) {           for (long long s = x; s < n; s += m2) {             long long u = a[s];             long long d = a[s + m] * w % mod;             a[s] = u + d;             if (a[s] >= mod) a[s] -= mod;             a[s + m] = u - d;             if (a[s + m] < 0) a[s + m] += mod;           }           w = w * base % mod;         }       }       for (auto& x : a)         if (x < 0) x += mod;     }     void ntt(vector<long long>& input) { _ntt(input, 1); }     void intt(vector<long long>& input) {       _ntt(input, -1);       const long long n_inv = mod_inv(((long long)(input).size()), mod);       for (auto& x : input) x = x * n_inv % mod;     }     vector<long long> convolution(const vector<long long>& a,                                   const vector<long long>& b) {       long long ntt_size = 1;       while (ntt_size < ((long long)(a).size()) + ((long long)(b).size()))         ntt_size *= 2;       vector<long long> _a = a, _b = b;       _a.resize(ntt_size);       _b.resize(ntt_size);       ntt(_a);       ntt(_b);       for (long long i = 0; i < (ntt_size); i++) {         (_a[i] *= _b[i]) %= mod;       }       intt(_a);       return _a;     }     vector<long long> powup(const vector<long long>& a, long long exponent) {       long long ntt_size = 1;       while (ntt_size < (((long long)(a).size()) * exponent)) ntt_size *= 2;       vector<long long> _a = a;       _a.resize(ntt_size);       ntt(_a);       for (long long i = 0; i < (ntt_size); i++) {         _a[i] = mod_pow(_a[i], exponent, mod);       }       intt(_a);       return _a;     }   };   vector<long long> mul(vector<long long> a, vector<long long> b, long long mod) {     for (auto& x : a) x %= mod;     for (auto& x : b) x %= mod;     NTT<167772161, 3> ntt1;     NTT<469762049, 3> ntt2;     NTT<1224736769, 3> ntt3;     auto x = ntt1.convolution(a, b);     auto y = ntt2.convolution(a, b);     auto z = ntt3.convolution(a, b);     const long long m1 = ntt1.get_mod(), m2 = ntt2.get_mod(), m3 = ntt3.get_mod();     const long long m1_inv_m2 = mod_inv<long long>(m1, m2);     const long long m12_inv_m3 = mod_inv<long long>(m1 * m2, m3);     const long long m12_mod = m1 * m2 % mod;     vector<long long> ret(((long long)(x).size()));     for (long long i = 0; i < (((long long)(x).size())); i++) {       long long v1 = (y[i] - x[i]) * m1_inv_m2 % m2;       if (v1 < 0) v1 += m2;       long long v2 = (z[i] - (x[i] + m1 * v1) % m3) * m12_inv_m3 % m3;       if (v2 < 0) v2 += m3;       long long constants3 = (x[i] + m1 * v1 + m12_mod * v2) % mod;       if (constants3 < 0) constants3 += mod;       ret[i] = constants3;     }     return ret;   }   vector<long long> exppoly(vector<long long> base, long long e, long long mod) {     vector<long long> ans = {1};     while (e > 0) {       if (e % 2 == 1) {         ans = mul(ans, base, mod);         e--;       } else {         base = mul(base, base, mod);         e /= 2;       }     }     return ans;   }   const long long MOD = 1000000007LL;   int main() {     ios_base::sync_with_stdio(false);     long long a, b, k, t;     cin >> a >> b >> k >> t;     vector<long long> v;     for (long long x = 0; x < 2 * k + 1; x++) v.push_back(1);     vector<long long> got = exppoly(v, t, MOD);     long long len = got.size();     vector<long long> suf = got;     for (long long x = len - 2; x >= 0; x--) suf[x] = (suf[x] + suf[x + 1]) % MOD;     long long ans = 0;     for (long long x = 0; x < len; x++) {       long long me = b + x;       long long youneed = max(0LL, me + 1 - a);       if (youneed >= len) continue;       ans += (got[x] * suf[youneed]);       ans %= MOD;     }     cout << ans << endl;   }   