#include <bits/stdc++.h>
 
using namespace std;
 
#define ll long long
#define endl "\n"
#define pll pair<ll, ll>
#define fs first
#define sc second
#define vll vector<ll>
 
const ll mod = 1e9 + 7;

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
    
    ll n, k;
    cin >> n >> k;

    vll v(n);
    for (ll i = 0; i < n; i++)
        cin >> v[i];

    if (k == 1 && n > 1)
    {
        cout << 0;
        return 0;
    }

    ll ans = 1;

    vll w(n);
    w[0] = v[0];
    for (ll i = 1; i < n; i++)
        w[i] = w[i-1] + v[i];

    for (ll i = 0; i < k-1; i++)
    {
        if (w[i] <= w[k-1]-w[i])
        {
            ans *= 2;
            ans %= mod;
        }
    }

    for (ll i = k; i < n; i++)
    {
        if (w[i-1] <= v[i])
        {
            cout << 0;
            return 0;
        }
        if (w[i-1] > w[n-1]-w[i-1])
        {
            ans *= 2;
            ans %= mod;
        }
        else if (i < n-1)
        {
            if (w[i-1] > v[i] + v[i+1])
            {
                ans *= 2;
                ans %= mod;
            }
        }
        else
        {
            ans *= 2;
            ans %= 1000000007;
        }
    }
    if (k == n)
    {
        ans *= 2;
        ans %= mod;
    }
    cout << ans;

    return 0;
}