#include<bits/stdc++.h> using namespace std; int s[1000010]; int a[1000010]; int main(){ int n, k, max1 = 0; scanf("%d%d", &n, &k); for (int i = 1; i <= n; i++){ scanf("%d", &a[i]); s[i] = s[i - 1] + a[i]; } for (int i = 1; i <= n - k; i++){ max1 = max(max1, s[i + k] - s[i - 1]); } printf("%d", max1); return 0; }