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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.*;
import java.util.*;


public class Main {

    private static BufferedReader br;
    private static StreamTokenizer st;
    private static PrintWriter pw;

    static final int INF = 1000000007;
    static final int MOD = 1000000007;

    private static void solve() throws IOException {
        int n = nextInt();
        int a[] = new int[n + 1];
        long res = 0;
        for (int i = 0; i <= n; i++) {
            a[i] = nextInt();
        }
        for (int i = 0; i < n; i++) {
            int b = nextInt();
            res += Math.min(b, a[i] + a[i + 1]);
            a[i + 1] -= Math.min(a[i + 1], Math.max(0, b - a[i]));
        }
        pw.println(res);
    }

    static long gcd(long a, long b) {
        if (a < b) {
            a ^= b;
            b ^= a;
            a ^= b;
        }
        while (b != 0) {
            long t = a % b;
            a = b;
            b = t;
        }
        return a;
    }

    static long inv(long t, long p) {
        return t == 1 ? 1 : (p - p / t) * inv(p % t, p) % p;
    }

    public static void main(String args[]) throws IOException {
//        System.out.println(System.getProperty("java.library.path"));

//        boolean oj = System.getProperty("ONLINE_JUDGE") != null;
//        if (!oj) {
//            System.setIn(new FileInputStream("src/in.txt"));
//            System.setOut(new PrintStream("out.txt"));
//        }
        br = new BufferedReader(new InputStreamReader(System.in));
        st = new StreamTokenizer(br);
        pw = new PrintWriter(new OutputStreamWriter(System.out));
        st.ordinaryChar('\'');
        st.ordinaryChar('\"');
        st.ordinaryChar('/');

//        long t = System.currentTimeMillis();
        solve();
//        if (!oj) {
//            pw.println("[" + (System.currentTimeMillis() - t) + "ms]");
//        }
        pw.flush();
    }

    private static long[] anLong(int n) throws IOException {
        long a[] = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = nextInt();
        }
        return a;
    }

    private static String next(int len) throws IOException {
        int b = br.read();
        while (b == '\n' || b == ' ' || b == '\r' || b == '\t') {
            b = br.read();
        }
        char ch[] = new char[len];
        ch[0] = (char) b;
        int idx = 1;
        while (idx < len && (b = br.read()) != ' ' && b != '\n' && b != '\r' && b != '\t') {
            ch[idx++] = (char) b;
        }
        return String.valueOf(ch).trim();
    }

    private static int nextInt() throws IOException {
        st.nextToken();
        return (int) st.nval;
    }

    private static long nextLong() throws IOException {
        return Long.parseLong(nextLine());
    }

    private static double nextDouble() throws IOException {
        st.nextToken();
        return st.nval;
    }

    private static String[] nextSS(String reg) throws IOException {
        return br.readLine().split(reg);
    }

    private static String nextLine() throws IOException {
        return br.readLine();
    }
}