#include<bits/stdc++.h>
using namespace std;
const long long mod=1e9+7;
int n,k;
long long ans;
long long dp[4001][4001];
void solve()
{
dp[1][1]=1;
for(int i=2;i<=n;i++)
{
for(int j=1;j<=k;j++)
{
dp[i][j]=dp[i-1][j]+dp[i-1][j-1]*(i-1)%mod;
dp[i][j]%=mod;
if(n==i)ans=(ans+dp[i][j])%mod;
}
}
cout<<ans<<endl;
}
int main()
{
cin>>n>>k;
solve();
return 0;
}
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