#include <cstdio>
const int mod = 1000000007;
int fast_pow(long long x, long long y)
{
	long long ans = 1;
	while (y)
	{
		if (y & 1)
			ans = (ans*x) % mod;
		x = (x*x) % mod;
		y >>= 1;
	}
	return ans;
}
int arrsum(int n, int k)
{
	if (n == 1) return 1;
	long long ans = arrsum(n >> 1, k);
	ans = ans + (fast_pow(k, n >> 1)*ans) % mod;
	if (n & 1) ans += fast_pow(k, n - 1);
	return ans%mod;
}
int main()
{
	freopen("sum.in", "r", stdin);
	freopen("sum.out", "w", stdout);
	int n, m, ans = 0;
	scanf("%d%d", &n, &m);
	for (int i = 1; i <= n; i++)
		ans = (ans + arrsum(m + 1, i) - 1) % mod;
	printf("%d", ans);
	return 0;
}