Problem:
Score : 300 points

Problem Statement

There are N+1 towns. The i-th town is being attacked by A_i monsters.

We have N heroes. The i-th hero can defeat monsters attacking the i-th or (i+1)-th town, for a total of at most B_i monsters.

What is the maximum total number of monsters the heroes can cooperate to defeat?

Constraints

All values in input are integers.

1 \leq N \leq 10^5

1 \leq A_i \leq 10^9

1 \leq B_i \leq 10^9

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_{N+1}
B_1 B_2 ... B_N

Output

Print the maximum total number of monsters the heroes can defeat.

Sample Input 1

2
3 5 2
4 5

Sample Output 1

9

If the heroes choose the monsters to defeat as follows, they can defeat nine monsters in total, which is the maximum result.

The first hero defeats two monsters attacking the first town and two monsters attacking the second town.

The second hero defeats three monsters attacking the second town and two monsters attacking the third town.

Sample Input 2

3
5 6 3 8
5 100 8

Sample Output 2

22

Sample Input 3

2
100 1 1
1 100

Sample Output 3

3

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <iostream>
#include <sstream>
#include <fstream>
#include <string>
#include <vector>
#include <tuple>
#include <deque>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <algorithm>
#include <functional>
#include <utility>
#include <bitset>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <numeric>
#include <string.h>
#define rep(i, x) for (int i = 0; i < (int)(x); i++)
#define repn(i, x) for (int i = 1; i <= (int)(x); i++)
#define repr(i, x) for (int i = ((int)(x) - 1); i >= 0; i--)
#define reprn(i, x) for (int i = ((int)(x)); i > 0; i--)
#define all(x) (x).begin,(x).end()
using namespace std;
typedef long long int64;
const double PI = 3.14159265358979323846;
const double EPS = 1e-12;
const int INF = 1<<29;
const long long INFL = 1e18;
const int MOD = 1000000007;
const int MAX = 210000;

int gcd(int a, int b) {
    return b != 0 ? gcd(b, a % b) : a;
}

//逆元を求める関数
long long fac[MAX], finv[MAX], inv[MAX];
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++) {
      fac[i] = fac[i-1] * i % MOD;
      inv[i] = MOD - inv[MOD%i] * (MOD/i) % MOD;
      finv[i] = finv[i-1] * inv[i] % MOD;
    }
}
//組み合わせ
long long COM (int n, int k) {
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n-k] % MOD) % MOD;
}

void solve() {
		long n; cin >> n;
		vector<long> a(n + 1);
		vector<long> b(n);
		rep(i, n + 1) {
			cin >> a[i];
		}
		rep(i, n) {
			cin >> b[i];
		}
		int ans = 0;
		rep(i, n) {
			//n番目の勇者でi番目のモンスターを倒しきれるだけ倒す
			long t = a[i] < b[i] ? a[i] : b[i];
			//倒したモンスターの数だけ力を消費する
			ans += t;
			b[i] -= t;
			//i + 1番目のモンスターについて、残った力で倒しきれるだけ倒す、全部倒せる場合は全部
			t = a[i + 1] < b[i] ? a[i + 1] : b[i];
			//倒した数だけモンスターの数を減少させる
			a[i + 1] -= t;
			ans += t;
		}
		cout << ans << endl;
    return;
}

int main() {
    solve();
    return 0;
}