#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);
ll n;
cin >> n;
ll x[n], y[n], tot = 0;
for (ll i = 0; i < n; i++)
cin >> x[i];
for (ll i = 0; i < n; i++)
{
cin >> y[i];
tot += y[i];
}
ll free = 0, ans = 0, u;
for (ll i = 0; i < n; i++)
{
u = min(free, y[i]);
free -= u;
y[i] -= u;
tot -= u;
ans += u;
if (x[i] > y[i])
{
free += x[i] - y[i];
x[i] = y[i];
}
}
free = 0;
for (ll i = 0; i < n; i++)
{
tot -= y[i];
u = min(free, y[i]);
free -= u;
y[i] -= u;
ans += u;
if (x[i] > tot)
{
free = tot;
ans -= max(y[i] - (x[i] - tot), 0ll);
}
else
{
free += x[i];
ans -= y[i];
}
}
cout << ans << endl;
return 0;
}
