#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

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

int dequee[5000010], a[5000010], n, k, st, dr;
long long sum;

int main()
{
    fin >> n >> k;
        for(int i = 1; i <= n; i++)
            fin >> a[i];
    st = 1; dr = 0;
    for(int i = 1; i <= n; i++)
    {
        while(dr >= st && a[i] <= a[dequee[dr]])
            dr--;
        dr++;
        dequee[dr] = i;
        if(dequee[st] == i - k)
            st++;
        if(i >= k)
            sum += a[dequee[st]];
    }
    fout << sum;
    return 0;
}