#pragma region
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
// File
ifstream fin("deque.in");
ofstream fout("deque.out");
#pragma endregion

int main() {
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int n, k;
    fin >> n >> k;

    vector<int> myDeque(1);
    int front = 1, back = 0;
    ll sum = 0;
    for (int i = 1; i <= n; i++) {
        int x;  fin >> x;
        myDeque.push_back(x);
        back++;
        if (back - front == k - 1) {
            ll currMin = myDeque[front];
            for (int j = front + 1; j <= back; j++)
                currMin = min(currMin, ll(myDeque[j]));
            sum += currMin;
            front++;
        }
    }
    fout << sum;

    return 0;
}