#include <fstream>
#include <deque>
using namespace std;

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

const int MaxN = 5000000 + 5;

deque<int> q;
int v[MaxN], n, k;

int main()
{
    fin >> n >> k;
    for (int i = 1; i <= n; ++i)
        fin >> v[i];

	for(int i = 1; i <= k - 1; ++i)
	{
		while(!q.empty() && v[q.back()] > v[i])
            q.pop_back();
        q.push_back(i);
    }

	long long sum = 0;
    for(int i = k; i <= n; ++i)
	{
        if(i - k == q.front())
            q.pop_front();

        while(!q.empty() && v[i] < v[q.back()])
			q.pop_back();
        q.push_back(i);

        sum += v[q.front()];
    }
    fout << sum;
    return 0;
}