// Skyqwq
#include <bits/stdc++.h>

#define pb push_back
#define fi first
#define se second
#define mp make_pair

using namespace std;

typedef long long LL;
typedef pair<int, int> PII;

template <typename T> bool chkMax(T &x, T y) { return (y > x) ? x = y, 1 : 0; }
template <typename T> bool chkMin(T &x, T y) { return (y < x) ? x = y, 1 : 0; }

template <typename T> void inline read(T &x) {
    int f = 1; x = 0; char s = getchar();
    while (s < '0' || s > '9') { if (s == '-') f = -1; s = getchar(); }
    while (s <= '9' && s >= '0') x = x * 10 + (s ^ 48), s = getchar();
    x *= f;
}

const int N = 5e3 + 5, P = 1e9 + 7;

int n, x, fact[N], infact[N], f[N], g[N];

int inline power(int a, int b) {
    int res = 1;
    while (b) {
        if (b & 1) res = (LL)res * a % P;
        a = (LL)a * a % P;
        b >>= 1;
    }
    return res;
}

void inline add(int &x, int y) {
    x += y;
    if (x >= P) x -= P;
}

void inline factPrework(int n) {
    fact[0] = infact[0] = 1;
    for (int i = 1; i <= n; i++) fact[i] = (LL)fact[i - 1] * i % P;
    infact[n] = power(fact[n], P - 2);
    for (int i = n - 1; i; i--) infact[i] = infact[i + 1] * (i + 1ll) % P;
}

int inline C(int a, int b) {
    if (a < b || a < 0 || b < 0) return 0;
    return (LL)fact[a] * infact[b] % P * infact[a - b] % P;
}

int inv2 = (P + 1) / 2;

int main() {
    factPrework(5e3 + 1);
    read(n), read(x);
    int ans = 0;
    for (int i = 0; i < n - x; i++) {
        for (int j = 0; j < x; j++) {
            if (!j) add(ans, 1ll * fact[i + 1] * C(n - x, i + 1) % P * C(x, j + 1) % P * fact[n - i - j - 2] % P);
            else {
                int gx = 1ll * fact[i + j + 1] * inv2 % P;
                add(ans, 1ll * gx * C(n - x, i + 1) % P * C(x, j + 1) % P * fact[n - i - j - 2] % P);
            }
        }
    }

    printf("%d\n", ans);
    return 0;
}