#include <iostream>
#include<fstream>
#define N 5000005
using namespace std;

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


int st,dr;
int a[N],n,k;

struct stiva
{
    int val,poz;
}s[N];

/*3
{1}
 */
void solve()
{
    int i;
    long long sum=0;
    for(i = 1; i <= n; ++i)
    {
        while(a[i] < s[dr].val && dr >= st)

            dr--;


        s[++dr].val=a[i];
        s[dr].poz=i;

        if(s[dr].poz - s[st].poz == k)
            st++;
        if(i >= k)
            sum = 1LL* (sum + s[st].val);

    }
    fout<<sum;
}



int main()
{
    int i;
   fin>>n>>k;
   for(i=1;i<=n;++i)
    fin>>a[i];
    solve();

    return 0;
}