#include <fstream>
#include <iostream>
#include <queue>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int main()
{
    int n, k, a;
    deque<pair<int, int>> min;
    long long minSum = 0;
    fin >> n >> k;
    for (int i = 0; i < n; ++i)
    {
        fin >> a;
        while (!min.empty() && min.back().first > a)
        {
            min.pop_back();
        }
        min.push_back({a, i});
        while (!min.empty() && min.front().second < i - k + 1)
        {
            min.pop_front();
        }
        if (i >= k - 1)
        {
            minSum += min.front().first;
        }
    }
    fout << minSum;
    return 0;
}