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];

        for (int i = 0; i < n + 1; i++) {
            monster[i] = sc.nextInt();
        }

        for (int i = 0; i < n; i++) {
            hero[i] = sc.nextInt();
        }

        long ans = 0;

        for (int i = 0; i < n; i++) {
            if (hero[i] <= monster[i]) {
                ans += hero[i];
            } else {
                ans += monster[i];
                hero[i] -= monster[i];
                if (hero[i] <= monster[i + 1]) {
                    ans += hero[i];
                    monster[i + 1] -= hero[i];
                } else {
                    ans += monster[i + 1];
                    monster[i + 1] = 0;
                }
            }
        }

        System.out.println(ans);

        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