#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main(){
    int n,l;
    cin>>n>>l;
    const ll mod=1e9+7;
    ll dp[n+1];
    dp[0]=1;
    dp[1]=1;
    ll ruiseki=2;
    for(int i=2;i<=n;i++){
        if(i-l>0){
            ruiseki=(ruiseki-dp[i-l-1]+mod)%mod;
        }
	    dp[i]=ruiseki;
        ruiseki=(ruiseki+dp[i])%mod;
    }
    cout<<dp[n]<<endl;
}