#include <fstream>
#include <vector>
#include <deque>

using namespace std;

ifstream be("deque.in");
ofstream ki("deque.out");

int main()
{
    int n, k;
    be >> n >> k;

    vector<int> v(n);

    for(int i = 0; i < n; i++)
    {
        be >> v[i];
    }

    deque<pair<int, int>> dq;

    long long ans = 0;

    for(int i = 0; i < n; i++)
    {
        while(!dq.empty() && dq.back().second >= v[i])
        {
            dq.pop_back();
        }

        dq.push_back({i, v[i]});

        if(dq.front().first <= i - k)
        {
            dq.pop_front();
        }

        if(i >= k - 1) ans += dq.front().second;
    }

    ki << ans;

    return 0;
}