#include<stdio.h>
#include<stdbool.h>
#include<malloc.h>

int min(int a, int b)
{
    return a>b?b:a;
}
long long Solve (long long k, int* arr ,int n) 
{
    long long out = 0;
    int i,j;
    for (i=j=0; i<n ;i++)
    {
        if (arr[i]<=0)
            continue;

        while(i-j>k)
            ++j;
        while(arr[i]!=0 && (i+k)>=min(n-1,j))
        {
            if(arr[j]>0)
            {
                j++;
                continue;
            }
            int x = min(arr[i],abs(arr[j]));
            arr[i]-=x;
            arr[j]+=x;
            if(arr[j]>=0)
                j++;
        }
    }
    for (i=0; i <n ;i++)
        out += abs(arr[i]);
    return out;
}

int main() 
{
    long long k;
    int n,i_arr;
    scanf("%d %lld", &n, &k);
    int *arr = (int *)malloc(n*sizeof(int));
    for(i_arr=0; i_arr<n; i_arr++)
        scanf("%d", &arr[i_arr]);
    printf("%lld", Solve(k, arr, n));
}