#include <fstream>

using namespace std;

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

int n, a[5000001], s[5000001], ind = 1, ii =1, k;
long long sm=0;

int main()
{
    fin >> n >> k;
    for (int i = 1; i<=n; i++)
    {
        fin >> a[i];
        if (i == 1)s[1]=1;
        else
        {
            while (a[s[ind]] > a[i] && ind >= ii)ind--;
            ind++;
            s[ind]=i;
            if (i == k)sm+=a[s[1]];
            else if (i > k)
            {
                if (s[ii] <= i - k)ii++;
                sm+=a[s[ii]];
            }
        }
    }
    fout << sm;
    return 0;
}