/**

     freopen("in.in", "r", stdin);

     freopen("my.out", "w", stdout);

 */

 //// /////////////////////////////

 #include <cstdio>

 const int N = ;

 int a[N], sum[N], Q[N], t, e = ;

 inline void max(int &a, const int b) {

     if(a < b) a = b;

     return;

 }

 int main() {

     //freopen("in.in", "r", stdin);

     //freopen("my.out", "w", stdout);

     int n, M;

     scanf("%d%d", &n, &M);

     for(int i = ; i <= n; i++) {

         scanf("%d", &a[i]);

         sum[i] = sum[i - ] + a[i];

     }

     /*

     for(int i = 1; i <= n; i++) {

         printf("%d ", sum[i]);

     }

     printf("\n");

     */

     int ans = -0x3f3f3f3f;

     for(int i = ; i <= n; i++) { /// !! 0

         Q[++t] = i;

         if(Q[e] < i - M) {

             e++;

         }

         max(ans, sum[i] - sum[Q[e]]);

         while(e < t && sum[i] <= sum[Q[t - ]]) {

             Q[--t] = i;

         }

     }

     printf("%d", ans);

     return ;

 }