#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 myDeque[5000005];

int main() {
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    int n, k = 0;
    scanf("%d%d", &n, &k);

    int front = 1, back = 0;
    ll sum = 0;
    for (int i = 1; i <= n; i++) {
        int x;
        scanf("%d", &x);
        myDeque[i] = 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++;
        }
    }
    printf("%lld", sum);

    fclose(stdin);
    fclose(stdout);
    return 0;
}