#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define F first
#define S second
#define endl '\n'
#define Mp make_pair
#define pb push_back
#define pf push_front
#define size(x) (ll)x.size()
#define all(x) x.begin(), x.end()
#define fuck(x) cout<<"("<<#x<<" : "<<x<<")\n"
const int N = 5e5 + 100, lg = 18;
const ll Mod = 1e9 + 7;
const ll inf = 1e18 + 10;
ll MOD(ll a, ll mod=Mod) {
a%=mod; (a<0)&&(a+=mod); return a;
}
ll poww(ll a, ll b, ll mod=Mod) {
ll res = 1;
while(b > 0) {
if(b%2 == 1) res = MOD(res * a, mod);
b /= 2;
a = MOD(a * a, mod);
}
return res;
}
ll n, k;
ll dp[5005][5005];
void work() {
cin>>n>>k;
dp[1][1] = 1;
for(ll i=2; i<=n; i++) {
for(ll j=1; j<=i; j++) {
dp[i][j] = MOD(dp[i-1][j] * j + dp[i-1][j-1] * (i - j + 1));
}
}
cout<<dp[n][k]<<endl;
}
void reset_work() {
return;
}
int main() {
ios_base::sync_with_stdio(false), cin.tie(0);
// cin>>t;
int tc = 1;
while(tc --) {
work();
reset_work();
}
return 0;
}
