#include <bits/stdc++.h>

using namespace std;

deque<int> q;
int a[5000003],n,k;
long long s;
int main()
{
    int i,x;
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>a[i];
    ///prelucrez primele k elemente
    for(i=1;i<=k;i++)
    {
        x=a[i];
        ///scot din q toate elementele mai mari sau egale cu x
        while(!q.empty() && x<=a[q.back()])
            q.pop_back();
        q.push_back(i);
    }
    s=s+a[q.front()];
    ///restul elementelor
    for(i=k+1;i<=n;i++)
    {
        x=a[i];
        while(!q.empty() && x<=a[q.back()])
            q.pop_back();
        q.push_back(i);
       ///verific daca s-a invechit un element
       if(i-q.front()>=k)
            q.pop_front();
       s=s+a[q.front()];
    }
    fout<<s;
    return 0;
}