#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i,a,b) for (int i = a; i <= b; i++)
#define per(i,a,b) for (int i = a; i >= b; i--)
#define pii pair<int,int>
#define pb push_back
#define fi first
#define se second
#define all(v) (v).begin(), (v).end()
const int MAXN = 3e5+10;
const int INF = 1e18+10;
const int MOD = 1e9+7;
int a[MAXN], b[MAXN];
void solve() {
int n; cin >> n;
rep(i,1,n) cin >> a[i];
rep(i,1,n) cin >> b[i];
set<pii> st;
int sum = 0;
rep(i,1,n) {
if(a[i] > 0) {
st.insert({i,a[i]});
}
sum += a[i];
}
int ans = 0;
rep(i,1,n) {
while(b[i]>0) {
auto it = st.upper_bound({i,-1});
if(it==st.begin()) break;
it--;
auto [id, cnt] = *it;
st.erase(it);
if(cnt > b[i]) {
st.insert({id,cnt-b[i]});
ans += b[i];
sum -= b[i];
a[i] -= b[i];
b[i] = 0;
} else {
b[i] -= cnt;
sum -= cnt;
ans += cnt;
a[i] = 0;
}
}
}
rep(i,1,n) {
sum -= min(a[i], b[i]);
}
cout << ans-sum << endl;
}
int32_t main() {
ios_base::sync_with_stdio(0); cin.tie(nullptr);
int tt = 1;
//cin >> tt;
while (tt--) solve();
return 0;
}
