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.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.*;

public class Main {
    static int n,m;
    static long dp[]  ,arr[];
    static boolean[] v;
    static LinkedList<Integer>[] adj;
    static int[] ans;

    public static void main(String[] args) throws IOException{
        Reader.init(System.in);
        int n = Reader.nextInt();
        int[] a = new int[n+1];
        int[] b= new int[n+1];
        for (int i = 0 ; i < n+1 ; i++){
            a[i] = Reader.nextInt();
        }
        for (int i = 0; i < n ; i++){
            b[i] =Reader.nextInt();
        }
        long ans = 0;
        for (int i = 0  ; i < n ; i++){
            int min1 = Math.min(a[i],b[i]);
            ans+= min1;
            a[i]-=min1;
            b[i]-=min1;
            int min2 = Math.min(a[i+1],b[i]);
            ans+=min2;
            a[i+1]-=min2;
            b[i]-=min2;
        }
        System.out.println(ans);

    }


}

class TrieNode{

    int[][] next = new int[2][(1000003)*30];
    int[] cnt = new int[(1000003)*30];
    int Idx = 1;
    int value;
    TrieNode[] arr = new TrieNode[2];

    void insert(int n){
        int cur = 0;
        for(int i = 30 - 1; i >= 0; --i) {
            int val = n >> i & 1;
            int nxt = next[val][cur];
            if (nxt == 0)
                nxt = next[val][cur] = Idx++;
            cur = nxt;
            cnt[cur]++;
        }
    }

    int query(int n , int k){
        int num = 0;
        int ans = 0;
        for(int i = 30 - 1; i >= 0; i--) {
            int val = n >> i & 1;
            if (((k >> i) & 1) == 0) {
                if(val==1) {
                    ans += cnt[next[0][num]];
                }
                else{
                    ans += cnt[next[1][num]];
                }
                num = next[val][num];
            }
            else {
                if (val==1) {
                    num = next[0][num];
                }
                else{
                    num = next[1][num];
                }
            }
            if (num == 0) {
                break;
            }
        }
        ans +=cnt[num];
        return ans;
    }

}

class Reader {
    static BufferedReader reader;
    static StringTokenizer tokenizer;

    /** call this method to initialize reader for InputStream */
    static void init(InputStream input) {
        reader = new BufferedReader(
                new InputStreamReader(input) );
        tokenizer = new StringTokenizer("");
    }

    /** get next word */
    static String next() throws IOException {
        while ( ! tokenizer.hasMoreTokens() ) {
            //TODO add check for eof if necessary
            tokenizer = new StringTokenizer(
                    reader.readLine() );
        }
        return tokenizer.nextToken();
    }

    static int nextInt() throws IOException {
        return Integer.parseInt( next() );
    }
    static long nextLong() throws IOException {
        return Long.parseLong( next() );
    }

    static double nextDouble() throws IOException {
        return Double.parseDouble( next() );
    }
}