#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

int N, K;
int64_t ans;
deque<pair<int64_t, int>> dq;

int main()
{
    in >> N >> K;

    for(int i = 1; i <= N; i++)
    {
        int64_t x;
        in >> x;

        while(!dq.empty() && dq.back().first >= x)
            dq.pop_back();

        dq.emplace_back(x, i);

        if(!dq.empty() && dq.front().second <= i - K)
            dq.pop_front();

        if(i >= K)
            ans += dq.front().first;
    }

    out << ans << '\n';

    return 0;
}