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

ifstream f("date.in");
ofstream g("date.out");
deque <int> d;

int a[5000001], i,j,s,n,k;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;++i)
        f>>a[i];

    for(i=1;i<=n;++i)
    {
      while(d.size() !=0 && a[i]<= a[d.back()]) d.pop_back();
        d.push_back(i);
        if( d.front()==i-k) d.pop_front();
        if (i>=k) s+=a[d.front()];

    }

    g<<s;
    return 0;
}