#include <fstream>
#include <deque>
#define maxn 5000002
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int n, k, v[maxn];
long long s;

void read()
{
    fin >> n >> k;
    for (int i = 1; i <= n; i++)
        fin >> v[i];
}

void write()
{
    fout << s;
}

void solve()
{
    deque <int> d;

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

int main()
{
    read();
    solve();
    write();
    return 0;
}