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

struct ceva
{
    int val, pos;
};

deque < ceva > deqmin;

int nums[5000001];

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

int n, k;
long long S;

void read()
{
    fin >> n;
    fin >> k;
    for(int i = 1; i <= n; i++)
    {
        fin >> nums[i];
        while(!deqmin.empty() && deqmin.back().val > nums[i])
            deqmin.pop_back();

        if(!deqmin.empty() && i - deqmin.front().pos + 1 > k)
            deqmin.pop_front();

        ceva nr;
        nr.val = nums[i];
        nr.pos = i;
        deqmin.push_back(nr);

        if(i >= k)
            S += deqmin.front().val;
    }
}

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