#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll=long long;
using ull=unsigned long long;
using ld=long double;
using i128=__int128;
using P=pair<ll,ll>;
template<typename T> using vc=vector<T>;
template<typename T> using vv=vc<vc<T>>;
using vl=vc<ll>;
using vvl=vc<vc<ll>>;
using vul=vc<ull>;
using vs=vc<string>;
using vb=vc<bool>;
#define rep(i,s,n) for(ll i=s;i<(n);i++)
#define Rep(i,s,n) for(ll i=n;i>=s;i--)
#define nall(x) x.begin(),x.end()
#define rall(a) a.rbegin(),a.rend()
#define pb push_back
#define eb emplace_back
#define pob pop_back
#define nexp(v) next_permutation(v)
#define prep(v) prev_permutation(v)
#define YES cout<<"Yes"<<endl
#define NO cout<<"No"<<endl
#define YN {cout<<"Yes"<<endl;}else{cout<<"No"<<endl;}
#define M1 cout<<"-1"<<endl
const long long INF=(1LL<<62)-(1LL<<31)-1;
#define endl '\n'
using mint=modint998244353;
using mint7=modint1000000007;
//vl dx={1,-1,0,0};vl dy={0,0,1,-1};
//vl dx={0,0,1,1,1,-1,-1,-1};vl dy={1,-1,0,1,-1,0,1,-1};
bool out_grid(ll i, ll j, ll h, ll w){return (!(0<=i && i<h && 0<=j && j<w));}
void chmin(ll &a,ll b){if(a>b)a=b;}
void chmax(ll &a,ll b){if(a<b)a=b;}
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}
ll ceil_div(ll a,ll b){return (a+(b-1))/b;}



int main(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	
	ll n,m;
    cin >> n >> m;
    vl a(n),b(n),d(n);
    rep(i,0,n)cin >> a[i];
    rep(i,0,n){
        cin >> b[i];
        d[i]=max(0LL,a[i]-b[i]);
    }
    ll sum=0,ans=0;
    rep(i,0,m)sum+=d[i];
    rep(i,0,n-m+1){
        chmax(ans,sum);
        sum-=d[i];
        sum+=d[i+m];
    }
    cout << ans << endl;
}