#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1000000;
int n, k;
long long a[MAXN + 5], sum[MAXN + 5];
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> k;
    a[1] = 0;
    for (int i = 2; i <= n; i++)
        cin >> a[i];
    // 预处理 sum[]
    sum[1] = 0;
    for (int i = 2; i <= n; i++)
        sum[i] = sum[i - 1] + a[i];
    // 找到长度为 k 的子段中，子段和最大的一段的和
    int l = 1, r = 1 + k;
    long long maxSumK = sum[r] - sum[l];
    for (; r <= n; l++, r++)
        maxSumK = max(maxSumK, sum[r] - sum[l]);
    // 答案为 sum[n] - maxSumK
    cout << sum[n] - maxSumK << "\n";
    return 0;
}