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

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

vector<int> v;

int main() {
    int n, k;
    fin >> n >> k;
    for (int i = 0; i < n; ++i) {
        int x;
        fin >> x;
        v.push_back(x);
    }
    long long sum = 0;
    for (int i = 0; i <= n - k; ++i) {
        int minVal = INT_MAX;
        for (int j = i; j < i + k; ++j) {
            minVal = min(minVal, v[j]);
        }
        sum += minVal;
    }
    fout << sum;
    return 0;
}