#pragma GCC optimize("O3,inline")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using namespace std;
using ll = long long;
#define int ll
using ii = pair<int, int>;
using iii = pair<ii, int>;
constexpr int INF = 1e18 + 5;
constexpr int MAXN = 300'000 + 5;
constexpr int MOD = 1e9 + 7;
signed main() {
ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
// solve st1 xd
/*
int N; cin >> N;
vector<int> X(N); for (int i = 0; i < N; ++i) cin >> X[i];
vector<int> Y(N); for (int i = 0; i < N; ++i) cin >> Y[i];
if (Y[0] >= X[0]) Y[0] -= X[0], X[0] = 0;
else X[0] -= Y[0], Y[0] = 0;
int delta = 0;
if (Y[0] > 0) {
X[1] -= Y[0];
delta += Y[0];
}
else {
}
*/
int N; cin >> N;
vector<int> X(N); for (int i = 0; i < N; ++i) cin >> X[i];
vector<int> Y(N); for (int i = 0; i < N; ++i) cin >> Y[i];
int sumY = 0; for (int i = 0; i < N; ++i) sumY += Y[i];
int sumX = 0; for (int i = 0; i < N; ++i) sumX += X[i];
int diff = sumX - sumY;
for (int i = N-1; i >= 0; --i) {
int sub = min(diff, X[i]);
X[i] -= sub;
diff -= sub;
}
int delta = 0;
int ptr1 = N-2;
for (int i = N-1; i >= 1; --i) {
ptr1 = min(ptr1, i - 1);
while (ptr1 >= 0) {
if (Y[i] >= X[ptr1]) {
Y[i] -= X[ptr1];
delta += X[ptr1];
X[ptr1] = 0;
ptr1--;
}
else {
X[ptr1] -= Y[i];
delta += Y[i];
Y[i] = 0;
break;
}
}
}
for (int i = 0; i < N; ++i) {
int sub = min(X[i], Y[i]);
X[i] -= sub;
Y[i] -= sub;
}
for (int i = 0; i < N; ++i) delta -= Y[i];
cout << delta;
}
