#include <fstream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <climits>
using namespace std;

int n, k;
int v[5000001];

int minime[8001];


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

int main()
{
    fin >> n >> k;
    int st = 1, dr = 0;
    int sum = 0;
    for (int i = 1; i <= n; i++)
    {
        dr++;
        fin >> v[i];
        if (dr - st == k)
        {
            //afisez cel mai mic elem si suma
            int minim = INT_MAX;
            for (int j = st; j < dr; j++)
            {
                minim = min(minim, v[j]);
            }
            sum += minim;
            st++;
        }
    }
    int minim = INT_MAX;
    for (int j = st; j <= dr; j++)
    {
        minim = min(minim, v[j]);
    }
    sum += minim;
    fout << sum;
    return 0;
}