#include <iostream>
#include <vector>
#include <set>
#include <queue>
#include <algorithm>
#include <climits>

using namespace std;

#define int long long

int twopow(int exponent) {
	int cR = 1;
	for (size_t i = 0; i < exponent; i++)
	{
		cR = (2 * cR) % 1000000007;
	}
	return cR;
}

signed main()
{
    int n, k;
	cin >> n >> k;
    k--;
	vector<int> inp(n);
	vector<int> prefix(n + 1);
	for (size_t i = 0; i < n; i++)
	{
		cin >> inp[i];
		prefix[i + 1] = prefix[i] + inp[i];
	}
	int twoPower = 0;
	for (size_t i = 0; i < n; i++)
	{
		if (2 * prefix[i] > prefix[k + 1]) {
			twoPower = i - 1;
			break;
		}
	}
	int twoPower2 = 0;
	for (size_t i = k+1; i < n+1; i++)
	{
		if (2 * prefix[i] > prefix[n]) {
			twoPower2 = (n-k) - (n - i + 1);
		}
	}
	if (k == n - 1) twoPower++;
	cout << twopow(twoPower + twoPower2);
	return 0;
}