#include <fstream>
#include <iostream>
#define maxn 5000002
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int n, k, v[maxn], d[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()
{
    int p = 1, u = 0; //initializare; p > u => deque vid

    for (int i = 1; i <= n; i++) {
        while (p <= u && v[i] <= v[d[u]])
            u--;
        d[++u] = i;
        if (d[p] == i - k)
            p++;
        if (i >= k)
            s += v[d[p]];
    }
}

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