#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <map>
#include <set>
#include <queue>
#include <iomanip>
#include <cstring>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i,n) for (int i = 0; i < int(n);i++)
using mint = modint1000000007;
mint dp[100001];
int main(){
  int n,l;
  cin >> n >> l;
  dp[0] = 1;
  for (int i = 0; i < n;i++){
    if (i > 0) dp[i] += dp[i-1]; 
    dp[i+1] += dp[i];
    if (i-l >= 0) dp[i+1] -= dp[i-l];
  }
  //for (int i = 0; i <= n;i++){
  //  cout << dp[i].val() << " ";
  //}
  //cout << endl;
  cout << dp[n].val() << endl;

  return 0;
}