// ~ Be Name Khoda ~
#include <bits/stdc++.h>
//#pragma GCC optimize ("Ofast")
//#pragma GCC target("avx2")
//#pragma GCC optimize("unroll-loops,O3")
using namespace std;
typedef long long ll;
#define pb push_back
#define mp make_pair
#define all(x) x.begin(), x.end()
#define fi first
#define se second
const int maxn = 3e3 + 10;
const int maxn5 = 3e3 + 10;
const int maxnt = 1.2e6 + 10;
const int maxn3 = 1e3 + 10;
const int mod = 1e9 + 7;
const ll inf = 1e18;
int ent[maxn][maxn], pw[maxn][maxn];
int f[maxn];
inline void fix(int &a){
if(a < 0)
a += mod;
if(a >= mod)
a -= mod;
}
int main()
{
ios_base::sync_with_stdio(false); cin.tie(0);
int n, k; cin >> n >> k;
if(n > 3000)
return 0;
ent[0][0] = 1;
for(int i = 1; i < maxn; i++){
ent[i][0] = 1;
for(int j = 1; j <= i; j++)
fix(ent[i][j] = ent[i - 1][j] + ent[i - 1][j - 1]);
}
for(ll i = 0; i <= n; i++){
pw[i][0] = 1;
for(int j = 1; j < maxn; j++)
pw[i][j] = pw[i][j - 1] * i % mod;
}
for(int i = 1; i <= k; i++) for(int j = 1; j <= i; j++)
fix(f[i] += (ll(ent[i][j]) * pw[j][n] % mod) * (i % 2 == j % 2 ? 1 : -1));
int ans = 0;
for(int i = 1; i <= k; i++){
fix(ans += (ll(f[i]) * ent[n - i][k - i] % mod) * (i % 2 == k % 2 ? 1 : -1));
//cout << i << ' ' << f[i] << endl;
}
cout << ans << endl;
}
