#include <fstream>
#include <deque>

#define MAX 5000050

using namespace std;

int v[MAX], n, k; long long s;
deque <int> dq;

void citire()
{
    ifstream in("deque.in");
    in>>n>>k;
    for(int i = 1; i <= n; i++) in>>v[i];
    in.close();
}

void solve()
{
    for(int i = 1; i <= n; i++)
    {
        while(!dq.empty() && v[i] < v[dq.back()]) dq.pop_back();
        dq.push_back(i);
        if(dq.front() == i - k) dq.pop_front();
        if(i >= k) s += v[dq.front()];
    }
}

void afisare()
{
    ofstream out("deque.out");
    out<<s;
    out.close();
}

int main()
{
    citire();
    solve();
    afisare();
    return 0;
}