#include<iostream>

#include<cstdio>

#include<cstring>

#include<algorithm>

#define maxn 100500

using namespace std;

long long n,k,sum[maxn],dp[maxn],a[maxn],c[maxn],q[maxn],l=,r=,ans=;

int main()

{

    scanf("%lld%lld",&n,&k);

    for (long long i=;i<=n;i++)

    {

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

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

    }

    c[]=-sum[];

    for (long long i=;i<=k;i++)

    {

        dp[i]=sum[i];ans=max(ans,dp[i]);

        c[i+]=dp[i]-sum[i+];

        while ((l<=r) && (c[q[r]]<=c[i])) r--;

        q[++r]=i;

    }

    for (long long i=k+;i<=n;i++)

    {

        while ((l<=r) && (q[l]<i-k)) l++;

        dp[i]=c[q[l]]+sum[i];ans=max(ans,dp[i]);

        c[i+]=dp[i]-sum[i+];

        while ((l<=r) && (c[q[r]]<=c[i])) r--;

        q[++r]=i;

    }

    printf("%lld\n",ans);

    return ;

}