#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);
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 delta = 0;
/*
for (int d = 1; d < N; ++d) {
for (int i = N-1; i >= d; --i) {
int ptr1 = i-d;
int sub = min(Y[i], X[ptr1]);
Y[i] -= sub;
X[ptr1] -= sub;
delta += sub;
}
}
*/
int ptr1 = 1;
for (int i = 0; i < N-1; ++i) {
ptr1 = max(ptr1, i + 1);
while (ptr1 < N) {
if (Y[ptr1] <= X[i]) {
X[i] -= Y[ptr1];
delta += Y[ptr1];
Y[ptr1] = 0;
ptr1++;
}
else {
Y[ptr1] -= X[i];
delta += X[i];
X[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;
}
