import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n + 1];
        int[] b = new int[n];
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < b.length; i++) {
            b[i] = sc.nextInt();
        }
        long hunteredNumber = 0;
        for (int i = 0; i < b.length; i++) {
            long left = Math.min(a[i], b[i]);
            long right = Math.min(a[i + 1], b[i] - left);
            a[i + 1] -= right;
            hunteredNumber += left + right;
        }
        System.out.println(hunteredNumber);
        sc.close();
    }
}
/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