#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define rng(i,c,n) for(int i=c;i<n;i++)
#define fi first
#define se second
#define pb push_back
#define sz(a) (int) a.size()
#define all(a) a.begin(),a.end()
#define vec(...) vector<__VA_ARGS__>
#define _3zlqvu8 ios::sync_with_stdio(0),cin.tie(0)
typedef long long ll;
typedef vector<int> vi;
typedef pair<int,int> pii;
void print(){cout<<'\n';}
template<class h,class...t>
void print(const h&v,const t&...u){cout<<v<<' ',print(u...);}

// snuke's mod int
template <ll mod>
struct modint{
	ll x;
	modint(ll x=0):x((x%mod+mod)%mod){}
	modint operator-()const{return modint(-x);}
	modint& operator+=(const modint a){if((x+=a.x)>=mod) x-=mod; return *this;}
	modint& operator-=(const modint a){if((x+=mod-a.x)>=mod) x-=mod; return *this;}
	modint& operator*=(const modint a){(x*=a.x)%=mod; return *this;}
	modint operator+(const modint a)const{modint res(*this); return res+=a;}
	modint operator-(const modint a)const{modint res(*this); return res-=a;}
	modint operator*(const modint a)const{modint res(*this); return res*=a;}
	modint pow(ll n)const{
		modint res=1,x(*this);
		while(n){
			if(n&1)res*=x;
			x*=x;
			n>>=1;
		}
		return res;
	}
	modint inv()const{return pow(mod-2);}
};

using mint=modint<1000000007>;

void slv(){
	int n,k;
	cin>>n>>k;

	vec(vec(mint)) dp(n+1,vec(mint)(k+1));
	dp[1][0]=1;
	dp[2][0]=1;
	dp[2][1]=1;
	rng(i,2,n){
		vec(mint) ps(k+1);
		rep(j,k+1){
			if(j){
				ps[j]+=ps[j-1];
			}
			ps[j]+=dp[i][j];
		}
		rep(j,k+1){
			dp[i+1][j]+=ps[j];
			if(j>=i+1){
				dp[i+1][j]-=ps[j-(i+1)];
			}
		}
	}
	print(dp[n][k].x);
}

signed main(){
_3zlqvu8;
	slv();
}