typedef long long ll;
typedef long double ld;
#include <bits/stdc++.h>
using namespace std;
#define int long long

signed main(){
    ll n,l;
    std::cin >> n>>l;
    vector<ll> dp(n+1),dp2(n+2);
    dp[0] = 1;
    dp2[1] = 1;

    const ll MOD = 1e9+7;
    for (int i = 1; i <= n; i++) {
        dp[i] = dp2[i]-dp2[max(0ll,i-l)]+MOD;
        dp[i] %= MOD;
        dp2[i+1] = dp2[i]+dp[i];
        dp2[i+1] %= MOD;
    }
    std::cout << dp[n] << std::endl;
}