//#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

const int NMAX = 5000005;
int v[NMAX], deck[NMAX], k, n, fr, bk;

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

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