#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

const long long mod = 1e9 + 7;

void to(long long &x, long long y) {
  x += y;
  if (x >= mod) x -= mod;
}

int main() {
  int n, K;
  cin >> n >> K;

  vector<long long> dp0(K + 2);
  dp0[0] = 1;

  for (int i = 0; i < n; i++) {
    vector<long long> dp1(K + 2);
    for (int j = 0; j <= K; j++) {
      // k = 0 .. min(i, K - j)
      
      to(dp1[j], dp0[j]);
      to(dp1[j + min(i, K - j) + 1], mod - dp0[j]);
    }
    for (int i = 0; i <= K; i++) {
      to(dp1[i + 1], dp1[i]);
    }
    dp0 = dp1;
  }

  long long ans = 0;
  for (int i = 0; i <= K; i++) {
    (ans += dp0[i]) %= mod;
  }

  cout << ans << endl;
}