import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int[] monster = new int[N + 1];
        int[] hero = new int[N];
        long count = 0;
        for (int i = 0; i < N + 1; i++) {
            monster[i] = sc.nextInt();
        }
        for (int i = 0; i < N; i++) {
            hero[i] = sc.nextInt();
        }
        for (int i = 0; i < N; i++) {
            if (monster[i] >= hero[i]) {
                count += hero[i];
            } else if (monster[i] + monster[i + 1] >= hero[i]) {
                count += hero[i];
                monster[i + 1] -= (hero[i] - monster[i]);
            } else if (monster[i] + monster[i + 1] < hero[i]) {
                count += monster[i] + monster[i + 1];
                monster[i + 1] = 0;
            }
        }
        System.out.println(count);

    }

}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz