#include <fstream>

using namespace std;

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

const long long N = 5000000;
long long v[N];
int dq[N];

int main()
{
    int st = 0, dr = -1, k, n;
    long long s = 0;
    fin >> n >> k;
    for(int i = 0; i < n; i++)
    {
        fin >> v[i];
        if(st <= dr && dq[st] == i - k)
            st++;

        while(st <= dr && v[i] <= v[dq[dr]])
        {
            dr--;
        }
        dq[++dr] = i;

        if(i >= k - 1)
            s += v[dq[st]];
    }
    fout << s;

    return 0;
}