#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

#include <atcoder/fenwicktree>
#include <atcoder/modint>
using mint = atcoder::modint1000000007;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int n, l;
  cin >> n >> l;
  atcoder::fenwick_tree<mint> dp(n + 1);
  dp.add(0, 1);
  for (int i = 1; i <= n; ++i) {
    dp.add(i, dp.sum(max(0, i - l), i));
  }
  cout << dp.sum(n, n + 1).val() << '\n';
  return 0;
}