#include <bits/stdc++.h>
using namespace std;
string np = "deque";
ifstream f(np + ".in");
ofstream g(np + ".out");

// #define f cin
// #define g cout

int n, k, v[5000003], q[5000003];
long long s;

int main()
{
    f >> n >> k;
    for (int i = 1; i <= n; i++)
        f >> v[i];

    int st = 1, dr = 0;
    for (int i = 1; i <= n; i++)
    {
        while (st <= dr and v[i] <= v[q[dr]])
            dr--;
        q[++dr] = i;
        if (q[st] == i - k)
            st++;
        if (i >= k)
            s += v[q[st]];
    }

    g << s;

    return 0;
}