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

deque<int> deq;
int nums[5000001];

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

int n, k, S;

void read()
{
    fin >> n;
    fin >> k;
    for(int i = 1; i <= n; i++)
    {
        fin >> nums[i];
        while(!deq.empty() && nums[deq.back()] > nums[i])
        {
            deq.pop_back();
        }
        deq.push_back(i);
        if(i - deq.front() == k)
            deq.pop_front();
        if(i >= k)
            S += nums[deq.front()];
    }
}

int main()
{
    read();
    fout << S;
}