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: Accepted)

#include <bits/stdc++.h>
using namespace std;

/* #pragma */
//#pragma GCC optimize("Ofast")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")


/*alias*/
#define F first
#define S second

#define y0 y3487465
#define y1 y8687969
#define j0 j1347829
#define j1 j234892
#define next asdnext
#define prev asdprev
#define itn int

/*template*/
template<class T>inline bool amax(T &a, const T &b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>inline bool amin(T &a, const T &b) { if (b < a) { a = b; return 1; } return 0; }

/* func */
int32_t GCD(int32_t a, int32_t b){return b ? GCD(b, a%b) : a;}
int64_t GCD(int64_t a, int64_t b){return b ? GCD(b, a%b) : a;}
int32_t LCM(int32_t a, int32_t b){return a * b / GCD(a, b);}
int64_t LCM(int64_t a, int64_t b){return a * b / GCD(a, b);}

/*struct*/
struct aaa {
	aaa() {
		cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20);
	};
}aaaaaaa;

/* const */
constexpr int32_t INF = 1001001001;
constexpr int64_t LINF = 1001001001001001001ll;
constexpr int32_t MOD = 1e9 + 7; //10^9
constexpr int64_t EPS = 1e-9;
constexpr int32_t dx[] = { 1, 1, 0, -1, -1, -1, 0, 1 }, dy[] = { 0, 1, 1, 1, 0, -1, -1, -1 };
//constexpr int32_t dx[] = {1, 0, -1, 0}, dy[] = {0, 1, 0, -1};
//Counterclockwise from the 6o'clock direction
//Take the x-axis downward and the y-axis right


//g++ -std=c++14 -Wall --pedantic-errors -o template template.cpp
//g++ -std=c++14 -Wall --pedantic-errors template.cpp
//chcp 65001

/*global*/



#define int int64_t
signed main()
{
	int n; cin >> n;
	vector<int> a(n+1);
	for(int i = 0, i_len = (int)n+1; i < i_len; ++i) cin >> a[i];
	
	vector<int> b(n);
	for(int i = 0, i_len = (int)n; i < i_len; ++i) cin >> b[i];

	int ans{};
	for(int i = 0, i_len = (int)n; i < i_len; ++i){
		int left = min(a[i], b[i]);
		ans += left;
		a[i] -= left;
		b[i] -= left;

		int right = min(a[i+1], b[i]);
		ans += right;
		a[i+1] -= right;
		b[i] -= right;
	}

	cout << ans << endl;
}