#include <fstream>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
const int DIM = 5000001;
int d[DIM], v[DIM];
int main()
{
    int n, k;
    cin >> n >> k;

    long long st = 0, dr = -1, s = 0;
    for(int i = 0; i < n; ++i)
    {
        cin >> v[i];

        if(st <= dr && d[st] == i - k)
        {
            ++st;
        }
        while(st <= dr && v[i] <= v[d[dr]])
        {
            --dr;
        }
        d[++dr] = i;
        if(i >= k - 1)
            s += v[d[st]];
    }

    cout << s;
    return 0;
}