#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

typedef long long ll;

const int nmax=5000005;

struct nr
{
    int poz;
    ll val;
};

int n,k;
ll a[nmax];

void read()
{
    fin>>n>>k;

    for(int i=1;i<=n;i++)
        fin>>a[i];
}

void solve()
{
    ll ans=0;

    deque <nr> d;

    for(int i=1;i<=n;i++)
    {
        while(!d.empty() && d.front().poz<=i-k)
            d.pop_front();

        while(!d.empty() && d.back().val>=a[i])
            d.pop_back();

        d.push_back({i,a[i]});

        if(i>=k)
            //fout<<d.front().val<<" ";
            ans+=d.front().val;
    }

    fout<<ans;
}

int main()
{
    read();
    solve();

    return 0;
}