#include <bits/stdc++.h>
using namespace std;
const int N = 4'000 + 10,
            M = 1'000'000'007;
int n, k;
int f[N][N];
int32_t main() { 
    cin.tie(0)->sync_with_stdio(0);
    cin >> n >> k;
    f[0][0] = 1;
    for (int i = 1; i <= n; ++i) { 
        for (int j = 1; j <= min(i, k); ++j) { 
            auto& ret = f[i][j];
            ret = (1ll * f[i - 1][j] * j % M);
            ret = (ret + 1ll * f[i - 1][j - 1] * (i - j + 1) % M) % M;
        }
    }
    
    cout << f[n][k] << "\n";
}
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