#include <bits/stdc++.h>
#define ll long long
#define ff first
#define ss second
#define inf INT_MAX
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define FAR(i, a, b) for (int i = (a); i >= (b); i--)
#define all(x) (x.begin(), x.end())
const int MOD = 1e9 + 7;
using namespace std;
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
int n;
cin >> n;
int x[n], y[n];
for (int i = 0; i < n; i++)
cin >> x[i];
for (int i = 0; i < n; i++)
cin >> y[i];
int h = 0, w = 0, s = 0;
for (int i = n - 1; i > -1; i--)
{
int x1 = min(w, x[i]);
x[i] -= x1;
w -= x1;
int x2 = min(s, x[i]);
s -= x2;
x[i] -= x2;
h += x1 + x2;
s += min(x[i], y[i]);
w += y[i] - min(x[i], y[i]);
}
cout << h - w << '\n';
return 0;
}
