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#include <bits/stdc++.h>

using std::cout;
using std::cin;
using std::ios_base;
using std::string;
using std::sort;
using std::max;
using std::min;
using std::vector;
using std::priority_queue;
using std::stack;
using std::endl;
using std::fixed;

#define be_faster_please ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define ll long long

ll mod = 1000000007;
ll tab [4000];

ll fast_pow(ll a, ll b)
{
    if (b == 0)
        return 1;
    if (b == 1)
        return a;
    if (b % 2 == 0)
    {
        ll temp = fast_pow (a, b / 2);
        return (temp * temp) % mod;
    }
    else
    {
        ll temp = fast_pow (a, b / 2);
        return (((temp * temp) % mod) * a) % mod;
    }
}

ll wyznacz (int x, ll m)
{
    if (x == 1)
        return 0;
    if (x == 2)
        return m;
    if (x == 3)
        return (m * m) % mod;
    ll ans = 0;
    ans += fast_pow(m - 1, x - 2);
    ans += (fast_pow(m - 1, x - 3) * m) % mod;
    ans %= mod;
  //  ans += ((x - 3) * fast_pow(m - 1, x - 4)) % mod;
    //ans %= mod;
    ans = (ans * m) % mod;
    for(int i = 2; i + 2 <= x; i++)
    {
        ll temp = 0;
        int n = x - i;
        if(n == 2)
            temp = m;
        else
        {
            
            temp += fast_pow(m - 1, n - 2);
         //   temp += (fast_pow(m - 1, n - 3) * m) % mod;
            temp %= mod;
            temp = (temp * m) % mod;
        }
        temp *= tab[i];
        temp %= mod;
        ans += temp;
        ans %= mod;
       // cout << i << ": " << temp << "\n";
    }
    return ans;
}

int main()
{
    be_faster_please;
    ll n, m;
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
    {
        tab[i] = wyznacz(i, m);
       // cout << tab[i] << "\n";
    }
    cout << tab[n];
    return 0;
}