#include <bits/stdc++.h>

using namespace std;

#define MP make_pair

const int MOD = 1e9 + 7;

typedef long long LL;
typedef pair<int, int> PII;
typedef long double LD;
typedef vector<int> VI;
typedef vector<VI> VVI;

#define all(x) (x).begin(), (x).end()
#define bitCount __builtin_popcount

const int N = 10005;
const LL inf = (LL)1e14;
const int inv2 = 500000004;

LL dp[N];
int c[N];

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  for (int i = 1; i <= n; ++i) {
    cin >> c[i];
  }
  fill(dp, dp + n + 1, inf);
  dp[0] = 0;
  for (int i = 1; i <= n; ++i) {
    LL &cost = dp[min(n, i + k)];
    cost = min(dp[max(0, i - k - 1)] + c[i], cost);
  }
  cout << dp[n];
  return 0;
}