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: Runtime Error)

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;

#define MAX(a,b) ((a)>(b)?(a):(b))
#define MIN(a,b) ((a)<(b)?(a):(b))
#define ABS(a) ((a)>(0)?(a):-(a))
#define rep(i,a,b) for(int (i)=int(a);(i)<int(b);(i)++)
#define rrep(i,a,b) for(int (i)=int(a);(i)>=int(b);(i)--)

#define put(a) cout << (a) << endl
#define puts(a) cout << (a) << " "

#define INF 1e9+1
#define MOD 1e9+7
#define INF64 1e18+1

#define F first
#define S second

#define Pii  pair<int,int>
#define Pll  pair<long long,long long>
#define Piii pair<int,pair<int,int>>
#define Plll pair<long long,pair<long long,long long>>

#define Vll(a,b,c)    vector<vector<long long>> (a)((b),vector<long long>((c))
#define Vlll(a,b,c,d) vector<vector<vector<long long>>> (a)((b),vector<vector<long long>>((c),vector<long long>((d)))

#define MAX_N 1000000

int main (void)
{
  int N;
  cin >> N;
  vector<long long int> A(N);
  vector<long long int> B(N);
  rep(i,0,N+1){
    cin >> A[i];
  }
  rep(i,0,N){
    cin >> B[i];
  }

  long long int ans=0;

  rep(i,0,N) {
    if (A[i] >= B[i]) {
      ans += B[i];
    } else {
      B[i] -= A[i];
      ans += A[i];
      if (A[i+1] >= B[i]) {
        A[i+1] -= B[i];
        ans += B[i];
      } else {
        ans += A[i+1];
        A[i+1] = 0;
      }
    }
  }


  put(ans);
  return 0;
}