#include <bits/stdc++.h>
#define int long long
#define pii pair<int,int>
#define vi vector<int>
#define ff first
#define ss second
#define sp << " " <<
#define all(x) x.begin(),x.end()
#define big(x) ((int)(x.size()))
using namespace std;
const int MOD = 1e9+7, LIM = 1e6+1, inf = 2e9;
const int N = 1e5+1;
int add(int x,int y) {
if ((x + y) >= MOD) return x + y - MOD;
return x + y;
}
int mult(int x,int y) {
return (1LL * x * y) % MOD;
}
int expo(int x,int y) {
if (!y) return 1;
int e = expo(x, y >> 1);
e = mult(e, e);
if (y & 1) e = mult(e, x);
return e;
}
void solve() {
int n,k;
cin >> n >> k;
k--;
int dp[n+1][n+1]{};
dp[0][0] = 1;
for (int i = 1;i<=n;i++) {
for (int j = 0;j<=i;j++) {
if(j)dp[i][j] = add(mult(dp[i-1][j],(j+1)),mult(dp[i-1][j-1],(i-j)));
else dp[i][j] = 1;
}
}
cout << dp[n][k] << '\n';
}
signed main() {
ios_base::sync_with_stdio(0); cin.tie(0);
#ifdef Dodi
freopen("in.txt", "r", stdin);
freopen("out.txt", "w", stdout);
#endif
int t = 1;
//cin >> t;
while (t --> 0) solve();
}
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