#include <algorithm>
#include <cassert>
#include <cstring>
#include <iostream>
#include <vector>

#define TRACE(x) std::cout << #x << " = " << x << "\n"
#define _ << " _ " <<

using namespace std;
template <int32_t P>
struct ModInt_t {
  static constexpr auto mod = P;

  int32_t value;

  static_assert(P < (1 << 30) - 1, "2xP must fit into 32-bit signed integer");

  ModInt_t() : value{0} {};

  explicit ModInt_t(int32_t v) : value(v) {
    if (value >= P || value <= -P) value %= P;
    if (value < 0) value += P;
  };

  explicit operator bool() const { return value != 0; }
  explicit operator int32_t() const { return value; }

  ModInt_t& operator+=(const ModInt_t& other) {
    value += other.value;
    if (value >= P) value -= P;
    return *this;
  }

  ModInt_t& operator-=(const ModInt_t& other) {
    value -= other.value;
    if (value < 0) value += P;
    return *this;
  }

  ModInt_t& operator*=(const ModInt_t& other) {
    int64_t result = static_cast<int64_t>(value) * other.value;
    value = static_cast<int32_t>(result % P);
    return *this;
  }

  static ModInt_t inverse(ModInt_t x) { return ModInt_t{inverse(x.value)}; }

 private:
  static int32_t inverse(int32_t a) {
    int32_t b = P, x = 1, y = 0;
    while (b != 0) {
      auto k = a / b;
      a -= k * b;
      std::swap(a, b);
      x -= k * y;
      std::swap(x, y);
    }
    assert(a == 1);
    if (x < 0) x += P;
    return x;
  }
};

template <int32_t P>
ModInt_t<P> operator+(const ModInt_t<P>& a, const ModInt_t<P>& b) {
  auto res = a;
  return res += b;
};

template <int32_t P>
ModInt_t<P> operator-(const ModInt_t<P>& a, const ModInt_t<P>& b) {
  auto res = a;
  return res -= b;
};

template <int32_t P>
ModInt_t<P> operator*(const ModInt_t<P>& a, const ModInt_t<P>& b) {
  auto res = a;
  return res *= b;
};

template <int32_t P>
bool operator==(const ModInt_t<P>& a, const ModInt_t<P>& b) {
  return a.value == b.value;
};

template <int32_t P>
std::ostream& operator<<(std::ostream& os, const ModInt_t<P>& a) {
  os << a.value;
  return os;
}

template <typename T>
struct MulMonoid {
  using value_type = T;
  constexpr static T identity() { return T{1}; }
  constexpr static T op(const T& a, const T& b) { return a * b; }
};

template <typename T, typename U, typename Monoid = MulMonoid<T>>
T power(T a, U n) {
  T r{Monoid::identity()};
  while (n > 0) {
    if (n % 2) r = Monoid::op(r, a);
    a = Monoid::op(a, a);
    n /= 2;
  }
  return r;
}

using ModInt = ModInt_t<1000000007>;

struct ModInverses {
  vector<ModInt> inv;

  ModInverses(int n) : inv(n, ModInt{0}) {
    auto mod = ModInt::mod;
    assert(n < mod);

    inv[1] = ModInt{1};
    for (int i = 2; i < n; ++i) {
      inv[i] = ModInt{0} - ModInt{mod / i} * inv[mod % i];
    }
  };
};

struct Factorial {
  vector<ModInt> fact;
  vector<ModInt> invfact;

  ModInt choose(int n, int k) { return fact[n] * invfact[k] * invfact[n - k]; }

  Factorial(int n) : fact(n, ModInt{0}), invfact(n, ModInt{0}) {
    ModInverses inv(n);

    fact[0] = invfact[0] = ModInt{1};
    for (int i = 1; i < n; ++i) {
      fact[i] = fact[i - 1] * ModInt{i};
      invfact[i] = invfact[i - 1] * inv.inv[i];
    }
  }
};

ModInt solve(int N, int A) {
  Factorial f(N + 1);

  ModInt ans{0};
  for (int k = 0; k <= A; ++k) {
    for (int p = 1; p <= k; ++p) {
      auto v = f.fact[p];
      v *= f.choose(k, p);

      v *= f.fact[p + N - A - 1] * f.invfact[p - 1];

      int c = max(0, A - k - 1);
      v *= f.fact[p + N - A + c] * f.invfact[p + N - A];

      if ((k - p) % 2)
        ans -= v;
      else
        ans += v;
    }
  }

  return ans;
}

int main() {
  std::ios_base::sync_with_stdio(false);
  int N, A;
  cin >> N >> A;

  auto ret = solve(N, A);
  cout << ret << "\n";
  return 0;
}


Measured memory_bytes: 120420