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

long long int n, k, minn, summ = 0, v[5000005];
int i, j, pos;

int main() {
    ifstream fin("deque.in");
    ofstream fout("deque.out");
	fin >> n >> k;
	for (i = 1; i <= n; ++i) {
        fin >> v[i];
	}
	for (i = 1, pos = i + k - 1; pos <= n; ++i, ++pos) {
        minn = 10000005;
        for (j = i; j <= pos; ++j) {
            if (v[j] < minn) {
                minn = v[j];
            }
        }
        summ = summ + minn;
	}
	fout << summ;
	return 0;
}