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


int n,k, v[5000009], deq[5000009], start ,END, i;
long long s;
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");

    f>>n>>k;

    for(i = 0;i < n;i++)
        f>>v[i];

    start = 0;END = -1;

    for(i=0;i<n;i++)
    {
        while(start < END && v[i] <= v[deq[END]])
            END--;

        deq[++END] = i;

        if(deq[start] == i - k)
            start++;

        if(i >= k - 1)
            s += v[deq[start]];
    }

    g<<s;

    return 0;
}