#include <stdio.h>
#include <stdlib.h>

inline int max(int x, int y)
{
    return x > y ? x : y;
}

int main()
{
    int n,i,a,k,smax;
    FILE * fp;
    fp = fopen("secv2.in","r");
    fscanf(fp,"%i",&n);
    fscanf(fp,"%i",&k);
    int sc = 0;
    int sum[n];
    int array[n];
    for(i = 0;i<n;i++)
    {
        fscanf(fp,"%i",&a);
        sc+=a;
        array[i] = a;
        sum[i] = sc;
    }
    sc = sum[k-1];
    for(i = 0;i<n;i++)
    {
        sc+=array[i];
        if(sc < sum[i] - sum[i-k])
        {
            sc = sum[i] - sum[i-k];
        }
        smax = max(smax, sc);
    }
    fclose(fp);
    fp = fopen("secv2.out","w");
    fprintf(fp,"%i",smax);
    fclose(fp);
    return 0;
}