#include <bits/stdc++.h>
using namespace std;
int N;
vector<int> x;
vector<int> y;
bool check(int c)
{
vector<int> v = y;
for (int i = 0; i < N; i++)
{
if (c > v[i]) {c -= v[i]; v[i] = 0; continue;}
v[i] -= c;
break;
}
int sum_x = 0, sum_y = 0;
for (int i = 0; i < N; i++)
{
sum_x += x[i], sum_y += v[i];
if (sum_x < sum_y) return false;
}
return true;
}
int get_ans(int c)
{
vector<int> v = y;
for (int i = 0; i < N; i++)
{
if (c > v[i]) {c -= v[i]; v[i] = 0; continue;}
v[i] -= c;
break;
}
int sum_x = 0, sum_y = 0;
int ans = 0;
for (int i = 0; i < N; i++)
{
sum_x += x[i], sum_y += v[i];
ans += min((sum_x - x[i]) - (sum_y - v[i]), v[i]);
}
return ans - c;
}
int main()
{
cin >> N;
x.resize(N), y.resize(N);
for (int i = 0; i < N; i++) cin >> x[i];
for (int i = 0; i < N; i++) cin >> y[i];
int l = 0, r = 0;
for (int i = 0; i < N; i++) r += y[i];
while (l < r) // first true
{
int m = (l + r) >> 1;
if (check(m)) r = m;
else l = m + 1;
}
int ans = get_ans(r);
int zw = 0;
for (int i = 0; i < N; i++)
{
if (y[i] != 0) {zw = i; break;}
}
if (check(y[zw])) ans = max(ans, get_ans(y[zw]));
cout << ans << '\n';
}
