#include <bits/stdc++.h>
using namespace std;
deque<int>q;
ifstream fin("deque.in");
ofstream fout("deque.out");
int a[5000005],n,k;
void Citire()
{
    int i;
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>a[i];
}
int main()
{
    int i,x;
    long long s=0;
    Citire();
    for(i=1;i<=k;i++)
    {
        x=a[i];
        while(!q.empty() and a[q.back()]>=x)
            q.pop_back();
        q.push_back(i);
    }
    s+=a[q.front()];
    for(i=k+1;i<=n;i++)
    {
        x=a[i];
        while(!q.empty() and a[q.back()]>=x)
            q.pop_back();
        q.push_back(i);
        if(i-k>=q.front())
            q.pop_front();
       s+=a[q.front()];
    }
    fout<<s<<"\n";
    fin.close();
    fout.close();
}