#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define mt make_tuple
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
#define pb push_back
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

const int MO = (int)1e9 + 7;
int N, K;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);

    cin >> N >> K;

    int L = N*(N - 1) / 2 + 1;
    vll cur(L + 1), nex(L + 1), sm(L + 1);
    cur[0] = 1;

    for (int i = N - 1; i >= 1; --i) {
        fill(all(nex), 0ll);
        rep(j, L)sm[j + 1] = (sm[j] + cur[j]) % MO;

        rep(r, L) {
            int l = max(0, r - i);
            nex[r] = (sm[r + 1] - sm[l] + MO) % MO;
        }
        swap(cur, nex);
    }

    ll ans = 0;
    rep(i, K + 1)(ans += cur[i]) %= MO;
    cout << ans << endl;
}