#include<bits/stdc++.h>
using namespace std;
using ll=long long;
int main()
{
    cin.tie(0)->sync_with_stdio(0);
    ll n,m;cin>>n>>m;
    vector<ll>a(n),b(n),d(n);
    for(auto&o:a)cin>>o;
    for(auto&o:b)cin>>o;
    for(int i=0;i<n;i++)d[i]=a[i]-b[i];
    ll ans=-1LL<<60,now=0,r=0;
    for(int i=0;i<n;i++)
    {
        while(r<n&&r-i<m)
        {
            now+=max(0ll,d[r]);
            r++;
        }
        ans=max(ans,now);
        now-=max(0ll,d[i]);
    }
    cout<<ans<<endl;
}