#include <bits/stdc++.h>
using namespace std;

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

vector <long long> sir;
long long n, k, sum = 0, minn = 10000000;

int main()
{
    cin >> n >> k;
    while(n--){
        int numar;
        fin >> numar;
        sir.push_back(numar);
    }

    for(int i = 0; i < sir.size() - k + 1; i++){
        minn = 10000000;
        for (int j = i; j < i + k; j++)
            minn = min(minn,sir[j]);

        sum+=minn;
    }
    fout << sum;
}