#include "bits/stdc++.h"
#include "homecoming.h"
using namespace std;
#define intl long long
intl solve(int n, int k, int *A, int *B) {
vector <intl> a, b, pref(n, 0);
function <intl(int)> get=[&](int idx) {
if(idx + k - 1 < n) return (pref[idx+k-1]-(idx?pref[idx-1]:0LL))*1LL;
else {
intl ans = (pref[n-1]-(idx?pref[idx-1]:0LL)) * 1LL;
ans += (pref[(idx+k-1)%n])*1LL;
return ans;
}
};
for(int i = 0; i < n; i ++) a.push_back(A[i]);
for(int i = 0; i < n; i ++) b.push_back(B[i]);
intl ans = 0;
for(int i = 0; i < n; i ++) {
if(i) pref[i] = pref[i-1];
pref[i] += (b[i] * 1LL);
}
// for(auto i : pref) cout << i << " ";
// cout << "\n";
for(int i = 0; i < n; i ++) {
// cout << a[i] - get(i) << " ";
ans += max(0LL, a[i] - get(i));
}
// cout << "\n";
return ans;
}
