#include<bits/stdc++.h>
using namespace std;
const int N = 3e5 + 10;
int n;
vector<int> x, y;
int solve1(vector<int> x, vector<int> y)
{
int ans = 0;
set<int> st;
for(int i = 0; i < n; i ++)
if(x[i] > 0)
st.insert(i);
for(int i = n - 1; i >= 0; i--)
{
while(y[i] > 0)
{
auto it = st.lower_bound(i);
if(it != st.begin())
{
it--;
int j = *it;
int mi = min(y[i], x[j]);
y[i] -= mi;
x[j] -= mi;
if(j < i)
ans += mi;
if(x[j] == 0) st.erase(j);
}
else
{
it--;
int j = *it;
int mi = min(y[i], x[j]);
y[i] -= mi;
x[j] -= mi;
if(j > i)
ans -= mi;
if(x[j] == 0) st.erase(j);
}
}
}
return ans;
}
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 sm = 0;
for(int i = 0; i < n; i ++)
sm += y[i];
for(int i = 0; i < n; i ++)
{
x[i] = min(sm, x[i]);
sm -= x[i];
}
int s1 = solve1(x, y);
int ans = 0;
int s = 0, e = n - 1;
for(int i = 0; i < n; i++)
{
while(y[i] > 0)
{
if(i > s)
{
int mi = min(y[i], x[s]);
x[s] -= mi;
y[i] -= mi;
if(i > s) ans += mi;
if(!x[s]) s++;
}
else
{
int mi = min(y[i], x[e]);
x[e] -= mi;
y[i] -= mi;
if(e > i) ans -= mi;
if(!x[e]) e--;
}
}
}
cout << max(ans, s1) << endl;
return 0;
}
