#include using namespace std; typedef long long ll; typedef pair l_l; typedef pair i_i; #define EPS (1e-7) #define INF (1e9) #define PI (acos(-1)) const ll mod = 1000000007; ll N, K; ll inv[1000000]; ll FactorialInv[1000000]; ll Factorial[1000000]; ll beki(ll a, ll b){ if(b == 0){ return 1; } ll ans = beki(a, b / 2); ans = ans * ans % mod; if(b % 2 == 1){ ans = ans * a % mod; } return ans; } void init_combination(){ inv[1] = 1; FactorialInv[1] = 1; Factorial[1] = 1; Factorial[0] = 1; FactorialInv[0] = 1; inv[1] = 0; for(int i = 2; i < 1000000; i++){ inv[i] = beki(i, mod - 2); Factorial[i] = Factorial[i - 1] * i % mod; FactorialInv[i] = FactorialInv[i - 1] * inv[i] % mod; } } ll combination(ll a, ll b){ if(a < 0) return 0; if(b < 0) return 0; if(b > a) return 0; if((a == b) || (b == 0)){ return 1; } ll ans = Factorial[a] * FactorialInv[b] % mod; ans = ans * FactorialInv[a - b] % mod; return ans; } int main() { //cout.precision(10); cin.tie(0); ios::sync_with_stdio(false); cin >> N >> K; init_combination(); ll ans = 0; for(ll i = 1; i <= N; i++) { ans += (i * combination(N-1, K) % mod) * Factorial[K]; ans %= mod; if(i < N) ans += (i * combination(N-2, K-2) % mod) * (inv[2] * Factorial[K] % mod); ans %= mod; cerr << i << " " << ans << endl; } cout << ans << endl; return 0; }