import java.util.Scanner;

public class Main {

    public static void main(String args[]) {

        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        Integer[] monster = new Integer[n + 1];
        for (int i = 0; i < n + 1; i++) {
            monster[i] = sc.nextInt();
        }
        Integer[] bravePower = new Integer[n];
        for (int i = 0; i < n; i++) {
            bravePower[i] = sc.nextInt();
        }

        long result = 0;
        for (int i = 0; i < n; i++) {
            if (monster[i] >= bravePower[i]) {
                result += bravePower[i];
            } else {
                result += monster[i];
                bravePower[i] -= monster[i];
                result += Math.min(bravePower[i], monster[i + 1]);
                monster[i + 1] = Math.max(0, monster[i + 1] - bravePower[i]);
            }
        }

        System.out.println(result);
    }
}

/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