#include <iostream>
#include <fstream>

#define max 5000005

using namespace std;

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

int v[max],deque[max],n,k,front,back;
long long s;

int main()
{
    fin >> n >> k;
    for(int i=1;i<=n;i++)
    fin >> v[i];
    front = 1;
    back = 0;
    for(int i=1;i<=n;i++)
    {
        while(front <= back && v[i] <= v[deque[back]]) back--;
        deque[++back] = i;
        if(deque[front] == i-k) front++;
        if(i >= k) s+=v[deque[front]];
    }
    fout << s;
    return 0;
}