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

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

deque <int> v;
deque <int> poz;

int n,k,sum,minn,c;

int main()
{
    f>>n>>k;
    for(int i=1;i<=k;i++)
    {
        f>>c;
        while(v.empty()==0 && v.back()>c){v.pop_back();poz.pop_back();}
        v.push_back(c);
        poz.push_back(i);
    }
    minn=v.front();
    sum+=minn;
    for(int i=k+1;i<=n;i++)
    {
        f>>c;
        while(v.empty()==0 && v.back()>c)
        {
             v.pop_back();
             poz.pop_back();
        }
        v.push_back(c);
        poz.push_back(i);
        if(poz.front()<i-k+1)
        {
            v.pop_front();
            poz.pop_front();
        }
        minn=v.front();
        sum+=minn;
    }
    g<<sum;
    return 0;
}