#include <fstream>
#include <deque>

using namespace std;

ifstream cin("deque.in");
ofstream cout("deque.out");

deque<pair<int, int> > q;

int main()
{
    long long ans = 0;
    int n, k;

    cin >> n >> k;

    for(int i = 1; i <= n; ++i)
    {
        int x;
        cin >> x;

        while(!q.empty() && q.back().first >= x)
        {
            q.pop_back();
        }

        q.push_back({x, i});

        if(q.front().second == i - k)
        {
            q.pop_front();
        }

        if(i >= k)
        {
            ans = ans + q.front().first;
        }
    }

    cout << ans;

    return 0;
}