#include <bits/stdc++.h>

using namespace std;
const int N = 3010;
const int INF = 0x3f3f3f3f;
int a[N];
int mi = INF;

int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 1; i <= n; i++)
    cin >> a[i];

  for (int i = 1; i <= n - m + 1; i++) {
    int sum = 0;
    for (int j = 0; j < m; j++)
      sum += a[i + j];
    mi = min(mi, sum);
  }
  cout << mi << endl;
  return 0;
}