#pragma GCC optimize("Ofast") #include using namespace std; typedef long long int ll; typedef unsigned long long int ull; mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count()); ll myRand(ll B) { return (ull)rng() % B; } template struct static_modint { using mint = static_modint; int x; static_modint() : x(0) {} static_modint(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {} mint &operator+=(const mint &rhs) { if ((x += rhs.x) >= mod) x -= mod; return *this; } mint &operator-=(const mint &rhs) { if ((x += mod - rhs.x) >= mod) x -= mod; return *this; } mint &operator*=(const mint &rhs) { x = (int)(1LL * x * rhs.x % mod); return *this; } mint &operator/=(const mint &rhs) { return *this = *this * rhs.inv(); } mint pow(long long n) const { mint _x = *this, r = 1; while (n) { if (n & 1) r *= _x; _x *= _x; n >>= 1; } return r; } mint inv() const { return pow(mod - 2); } mint operator+() const { return *this; } mint operator-() const { return mint() - *this; } friend mint operator+(const mint &lhs, const mint &rhs) { return mint(lhs) += rhs; } friend mint operator-(const mint &lhs, const mint &rhs) { return mint(lhs) -= rhs; } friend mint operator*(const mint &lhs, const mint &rhs) { return mint(lhs) *= rhs; } friend mint operator/(const mint &lhs, const mint &rhs) { return mint(lhs) /= rhs; } friend bool operator==(const mint &lhs, const mint &rhs) { return lhs.x == rhs.x; } friend bool operator!=(const mint &lhs, const mint &rhs) { return lhs.x != rhs.x; } friend ostream &operator<<(ostream &os, const mint &p) { return os << p.x; } friend istream &operator>>(istream &is, mint &a) { int64_t t; is >> t; a = static_modint(t); return (is); } }; const unsigned int mod = 1e9 + 7; using modint = static_modint; modint mod_pow(ll n, ll x) { return modint(n).pow(x); } modint mod_pow(modint n, ll x) { return n.pow(x); } template struct Comination { vector p, invp; Comination(int sz) : p(sz + 1), invp(sz + 1) { p[0] = 1; for (int i = 1; i <= sz; ++i) { p[i] = p[i - 1] * i; } invp[sz] = p[sz].inv(); for (int i = sz - 1; i >= 0; --i) { invp[i] = invp[i + 1] * (i + 1); } } T comb(int n, int r) { if (r < 0 or n < r) return 0; return p[n] * invp[n - r] * invp[r]; } T big_comb(T n, int r) { T res = invp[r]; for (int i = 0; i < r; ++i) { res *= (n - i); } return res; } }; using Comb = Comination; Comb comb(1 << 20); int main() { ios::sync_with_stdio(false); cin.tie(nullptr); int n, s, k; cin >> n >> s >> k; for (int i = 0; i < n; ++i) { s -= k * i; } if (s < 0) { cout << 0 << endl; } else { vector dp(s + 1); dp[0] = 1; for (int i = n; i >= 1; --i) { for (int j = i; j <= s; ++j) { dp[j] += dp[j - i]; } } cout << dp[s] << endl; } }