#include <bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n, t;
deque<pair<int, int>> dq;
long long rez;
int32_t main()
{
    f >> n >> t;
    for (int i = 1, x; i <= n; i++)
    {
        f >> x;
        while (!dq.empty() && dq.back().first > x)
            dq.pop_back();
        dq.push_back({x, i});
        if (dq.front().second == i - t)
            dq.pop_front();
        if (i >= t)
            rez += dq.front().first;
    }
    g << rez;
    return 0;
}