#include <limits.h>
#include <fstream>
using namespace std;

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

const int MAX_LEN = 5000000;
int v[MAX_LEN + 1], ps[MAX_LEN + 1];

int main() {
    int n, k;
    fin >> n >> k;
    for (int i = 1; i <= n; ++i) {
        fin >> v[i];
    }
    int minNum = INT_MAX, sum = 0;
    for (int i = 1, j = k; j <= n; ++i, ++j) {
        for (int x = i; x <= j; ++x) {
            if (v[x] < minNum) {
                minNum = v[x];
            }
        }
        sum += minNum;
        minNum = INT_MAX;
    }
    fout << sum;
}