#include <iostream>
#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int a[5000001],d[5000001],n,start,finish,i,k;
long long s;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>a[i];
    }
    start=1;
    finish=0;
    for(i=1;i<=n;i++)
    {
        while(start<=finish && a[i]<=a[d[finish]])
        {
            finish--;
        }
        finish++;
        d[finish]=i;
        if(d[start]==i-k)
        {
            start++;
        }
        if(i>=k)
        {
            s=s+a[d[start]];
        }
    }
    g<<s;
    return 0;
}