#include <iostream>
#include <fstream>
#define int long long

using namespace std;

int v[5000001], dequeue[5000001];

signed main()
{
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    int n, k, i, f = 1, b = 0, s = 0;
    cin >> n >> k;
    for(i = 1; i <= n; i++)
    {
        cin >> v[i];
    }
    for(i = 1; i <= n; i++)
    {
        while(f <= b && v[i] <= v[dequeue[b]])
        {
            b--;
        }
        b++;
        dequeue[b] = i;
        if(dequeue[f] == i - k)
        {
            f++;
        }
        if(i >= k)
        {
            s += v[dequeue[f]];
        }
    }
    cout << s;
    return 0;
}