summy

#include <iostream>
#define P 1000000007
#define ll long long
using namespace std;
ll n, k, suma, i, j, sol, y, numarator, numitor;

void gcd(ll &x, ll &y, ll a, ll b)
{
     if (!b)
         x = 1, y = 0;
     else
     {
         gcd(x, y, b, a % b);
         ll aux = x;
         x = y;
         y = aux - y * (a / b);
     }
}

ll invers(ll x)
{
    ll ins, inv = 0;
    gcd(inv, ins, x, P);
    if (inv <= 0)
       inv = P + inv % P;
    return inv;
}

ll pu(ll b, ll e)
{
    if(e == 0) return 1;
    else
    if(e % 2 == 0)
    {
        ll x = pu(b,e / 2);
        return (x * x) % P;
    }
    else return (b * pu(b,e-1)) % P;
}

int main()
{
    cin >> n >> k;
    if(n <= 100000)
    {
        sol = 0;
        for(i = 1; i <= n; i++)
            sol = (sol + pu(i,k)) % P;
    }
    else
    {
        suma = 1;
        numarator = 1;
        numitor = 1;
        for(i = 2; i <= k+2; i++)
        {
            numarator = (numarator*(n-i)) % P;
            numitor = (numitor*(1-i)) % P;
        }
        if(numitor < 0) numitor += P;
        sol = (numarator*invers(numitor)) % P;
        for(i = 2; i <= k+2; i++)
        {
            suma = (suma + pu(i,k)) % P;
            numarator = (numarator*(n-i+1)) % P;
            numarator = (numarator*invers(n-i)) % P;
            numitor = (numitor*(i-1)) % P;
            numitor = (-numitor*invers(k+3-i)) % P;
            if(numitor < 0) numitor += P;
            y = (numarator*invers(numitor)) % P;
            sol = (sol + suma * y) % P;
        }
    }
    cout << sol;
    return 0;
}