#include <fstream>
#include <cmath>

using namespace std;

ifstream fin("transport.in");
ofstream fout("transport.out");

int main()
{
    int n, k, s = 0, maxi = 0, x;

    fin >> n >> k;

    for(int i = 0; i < n; i++)
    {
        fin >> x;

        s += x;

        if(x > maxi)
            maxi = x;
    }

    if(n == k)
        fout << maxi;
    else {
            int z = s / k;
            fout << min(z, maxi) * 2 - max(z, maxi);
    }
}