#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
using ll = long long;
using graph = vector<vector<int>>;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
vector<int> dh = {-1,0,1,0,-1,1,1,-1};
vector<int> dw = {0,1,0,-1,1,1,-1,-1};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  int n, m; cin >> n >> m;
  vector<ll> a(n); rep(i, n) cin >> a.at(i);
  vector<ll> b(n); rep(i, n) cin >> b.at(i);
  vector<ll> r(n+1, 0);
  ll ans = 0;
  for(int i=1;i<=n;i++){
    r.at(i) = r.at(i-1) + max((ll)0, a.at(i-1)-b.at(i-1));
  }
  for(int i=0;i<=n-m;i++){
    ans = max(ans, r.at(i+m) - r.at(i));
  }
  cout << ans << "\n";
  return 0;
}