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

ifstream f("deque.in");
ofstream g("deque.out");

int a[5000001];
int Deque[5000001];
int n,k;

void citire()
{
    int i,j;
    int fata =0, spate = 0;
    long long total = 0;
    f>>n>>k;

    for(i = 1; i<=n; ++i)
        f>>a[i];

    for(i = 1; i<=n; ++i)
    {
        while( fata <= spate && a[i] <= a[ Deque[spate] ] )
            spate--;
        Deque[++spate] = i;
        if( Deque[fata] <= i-k )
            fata++;
        if( i>=k) total += a[ Deque[fata]];

    }

    g<<total;
}

int main()
{
    citire();


    return 0;
}