#include "bits/stdc++.h"
#include "atcoder/all"
using namespace std;
using namespace atcoder;
using mint = modint1000000007;
const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
//const bool debug = false;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
struct combination {
	vector<mint> fact, ifact;
	combination(int n) :fact(n + 1), ifact(n + 1) {
		assert(n < mod);
		fact[0] = 1;
		for (int i = 1; i <= n; ++i) fact[i] = fact[i - 1] * i;
		ifact[n] = fact[n].inv();
		for (int i = n; i >= 1; --i) ifact[i - 1] = ifact[i] * i;
	}
	mint operator()(int n, int k) {
		return com(n, k);
	}
	mint com(int n, int k) {
		//負の二項係数を考慮する場合にコメントアウトを外す
		//if (n < 0) return com(-n, k) * (k % 2 ? -1 : 1);
		if (k < 0 || k > n) return 0;
		return fact[n] * ifact[k] * ifact[n - k];
	}
	mint inv(int n, int k) {
		//if (n < 0) return inv(-n, k) * (k % 2 ? -1 : 1);
		if (k < 0 || k > n) return 0;
		return ifact[n] * fact[k] * fact[n - k];
	}
	mint p(int n, int k) {
		return fact[n] * ifact[n - k];
	}
}c(2000005);
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n, m; cin >> n >> m;
	mint ansl = 0;
	vector<mint>sumc(n + 1);
	sumc[0] = 0;
	rep(i, n)sumc[i + 1] = sumc[i] + c(n, i);
	{
		rep2(i, m, n + 1) {
			int a = i;
			int b = n - i;
			// t <= b - a
			if (b - a > 0)ansl += c(n, a) * (b - a);
			// b - a  < t <=  b
			//rep2(j, max(1, b - a + 1), b + 1)ansl += c(n, b - j);
			ansl += sumc[(b-(max(1, b - a + 1))) + 1] - sumc[0];
			// t > b
			// + 0
		}
	}
	mint ansn = 0;
	rep2(i, m, n + 1) ansn += c(n, i) * n;
	mint ansr = 0;
	{
		rep2(i, m, n + 1) {
			int a = n - i;
			int b = i;
			// t <= b - a
			if (b - a > 0)ansr += c(n, a) * (b - a);
			// b - a  < t <=  b
			//rep2(j, max(1, b - a + 1), b + 1)ansr += c(n, b - j);
			ansr += sumc[(b - (max(1, b - a + 1))) + 1] - sumc[0];
			// t > b
			// + 0
		}
	}
	mint ans = ansl + ansn + ansr;
	cout << ans.val() << endl;
	return 0;
}