#include<bits/stdc++.h>
using namespace std;

using ll = long long;

//constant
const ll MOD = 1e+9 + 7;
const double EPS = 1e-10;

#define REP(i, n) for (ll i = 0; i < n; i++)
#define FOR(i, s, e) for (ll i = s; i < e; i++)
#define ALL(x) (x).begin(),(x).end()
#define RALL(x) (x).rbegin(), (x).rend()

//debug
#define DUMP(x)  cerr << #x << " = " << (x) << endl;
#define DEBUG(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl;

// view vector
template<typename T> void view(T e) { std::cout << e << std::endl; }
template<typename T> void view(const std::vector<T>& v) { for (const auto& e : v) { std::cout << e << " "; } std::cout << std::endl; }
template<typename T> void view(const std::vector<std::vector<T> >& vv) { for (const auto& v : vv) { view(v); } }

// DP
template<class T>bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }

// ***************************************

// modint: mod 計算を int を扱うように扱える構造体
const ll inf = 1LL << 60;

struct Mint {
    ll v;
    ll _mod;
    Mint() : v(0) {}
    Mint(signed v, ll _mod = MOD) : v(v), _mod(_mod) {}
    Mint(ll t, ll _mod = MOD) : _mod(_mod) {
        v = t % _mod;
        if (v < 0)
            v += _mod;
    }

    Mint pow(ll k) {
        Mint res(1), tmp(v);
        while (k) {
            if (k & 1)
                res *= tmp;
            tmp *= tmp;
            k >>= 1;
        }
        return res;
    }
    static Mint add_identity() { return Mint(0); }
    static Mint mul_identity() { return Mint(1); }
    Mint inv() { return pow(_mod - 2); }

    Mint& operator+=(Mint a) {
        v += a.v;
        if (v >= _mod)
            v -= _mod;
        return *this;
    }
    Mint& operator-=(Mint a) {
        v += _mod - a.v;
        if (v >= _mod)
            v -= _mod;
        return *this;
    }
    Mint& operator*=(Mint a) {
        v = v * a.v % _mod;
        return *this;
    }
    Mint& operator/=(Mint a) { return (*this) *= a.inv(); }

    Mint operator+(Mint a) const { return Mint(v) += a; };
    Mint operator-(Mint a) const { return Mint(v) -= a; };
    Mint operator*(Mint a) const { return Mint(v) *= a; };
    Mint operator/(Mint a) const { return Mint(v) /= a; };

    Mint operator-() const { return v ? Mint(_mod - v) : Mint(v); }

    bool operator==(const Mint a) const { return v == a.v; }
    bool operator!=(const Mint a) const { return v != a.v; }
    bool operator<(const Mint a) const { return v < a.v; }
};
ostream& operator<<(ostream& os, Mint m) { return os << m.v; }

Mint nCk(int n, int k) {
    Mint ret = 1;
    for (int i = n; i > n - k; --i) {
        ret *= i;
    }
    for (int i = 1; i <= k; ++i) {
        ret /= i;
    }
    return ret;
}

int main(void) {

    int n, k;
    cin >> n >> k;

    Mint ans = 0;
    ans += 1;
    ans += Mint(n) * (n - 1);
    
    ll end = min(k+1, n);
    Mint nck = Mint(n) * (n - 1) / 2;
    Mint nck2 = Mint(n - 1) * (n - 2) / 2;
    FOR(i, 2, end) {
        ans += (nck * nck2);
        nck *= (n - i);
        nck /= (i + 1);
        nck2 *= (n - i - 1);
        nck2 /= (i + 1);
    }

    cout << ans.v << endl;
    
	return 0;
}

Measured memory_bytes: 256