#include <iostream>
using namespace std;

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

int main() {
	cin >> n >> k;
	for (i = 1; i <= n; ++i) {
        cin >> v[i];
	}
	for (i = 1, pos = i + k - 1; pos <= n; ++i, ++pos) {
        minn = 10000005;
        for (int j = i; j <= pos; ++j) {
            if (v[j] < minn) {
                minn = v[j];
            }
        }
        summ = summ + minn;
	}
	cout << summ;
	return 0;
}