#include <iostream>
#include <fstream>
#include <deque>
#define MAXN 5000041
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int a[MAXN],n,k;
long long s=0;
int main()
{
    deque<int>d;

    in>>n>>k;
    for(int i=1; i<=n; i++)
        in>>a[i];
    for(int i=1; i<=n; i++)
    {
        if(i<k)
        {
            while(!d.empty()&& a[i]<=a[d.back()])
                d.pop_back();
            d.push_back(i);
        }
        else
        {
            while(!d.empty()&&a[i]<=a[d.back()])
                d.pop_back();
            d.push_back(i);
            if(d.front()<=i-k)
                d.pop_front();
            s+=a[d.front()];
        }

    }
    out <<s;
    return 0;
}