#include <bits/stdc++.h>
using namespace std;
 
long long n, k, a[1000005];
int main(){
    cin >> n >> k;
    for(int i = 1; i <= n; i++) cin >> a[i];
    long long res = 0, sum = 0;
 
    //Cửa sổ đầu tiên
    for(int i = 1; i <= k; i++){
        sum = sum + a[i];
    }
 
    //Kết quả cho cửa sổ đầu tiên
    res = max(res, sum);
 
    //Các cửa sổ tiếp theo
    int i = 1;
    for(int j = k + 1; j <= n; j++){
        sum = sum + a[j];
        sum = sum - a[i];
        res = max(res, sum);
        i++;
    }
 
    cout << res;
    return 0;
}

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NyAzCi00IDUgNiAtMyA0IC0yIDE=

7 3
-4 5 6 -3 4 -2 1