#include<bits/stdc++.h>
// #include<atcoder/all>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rrep(i, n) for (int i = n - 1; i >= 0; i--)
#define FOR(i,s, n) for (int i = (s); i < (n); i++)
#define ALL(x) x.begin(),x.end()
#define rALL(x) x.rbegin(),x.rend()
using ll = long long;
using ld = long double;
using Graph = vector<vector<int>>;
// using mint = atcoder::modint998244353;
// using Mint = atcoder::modint1000000007;
const ll INF = 1LL << 60;
const ll inf = 1E9 + 7;
const ll MOD = 998244353;
const ll mod = 1E9 + 7;
const ll int_max = 1LL << 32;
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b;return true; }return false; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b;return true; }return false; }
template <class T>inline ll pair2idx(T x, T y, T n) { return (ll)x * n + y; }
template <class T>inline pair<int, int> idx2pair(T idx, T n) { return { idx / n, idx % n }; }

long long _pow(long long x, long long n) {
    long long ret = 1;
    while (n > 0) {
        if (n & 1) ret *= x;
        x *= x;
        n >>= 1;
    }
    return ret;
}

int main(){
    int n,m;cin>>n>>m;
    vector<int>a(n),b(n);
    rep(i,n)cin>>a[i];
    rep(i,n)cin>>b[i];
    ll now_sum=0;
    rep(i,m)now_sum+=max(a[i]-b[i],0);
    ll ans=0;
    rep(i,n-m){
        chmax(ans,now_sum);
        now_sum-=max(a[i]-b[i],0);
        now_sum+=max(a[i+m]-b[i+m],0);
    }
    chmax(ans,now_sum);
    cout << ans<<endl;
}