import java.util.*;

public class Main {

    public static void main(String[] args) {
        // write your code here
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int[] a = new int[n + 1];

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

        long sum = 0;

        for (int i = 0; i < n; i++) {
            int b = sc.nextInt();
            int buster = Math.min(a[i], b);
            int secondBuster = Math.min(a[i + 1], b - buster);
            a[i + 1] -= secondBuster;
            sum += buster + secondBuster;
        }

        System.out.println(sum);
    }
} import java.util.*; util.* java public class Main {

    public static void main(String[] args) {
        // write your code here
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int[] a = new int[n + 1];

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

        long sum = 0;

        for (int i = 0; i < n; i++) {
            int b = sc.nextInt();
            int buster = Math.min(a[i], b);
            int secondBuster = Math.min(a[i + 1], b - buster);
            a[i + 1] -= secondBuster;
            sum += buster + secondBuster;
        }

        System.out.println(sum);
    }
} Main public static void main(String[] args) {
        // write your code here
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int[] a = new int[n + 1];

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

        long sum = 0;

        for (int i = 0; i < n; i++) {
            int b = sc.nextInt();
            int buster = Math.min(a[i], b);
            int secondBuster = Math.min(a[i + 1], b - buster);
            a[i + 1] -= secondBuster;
            sum += buster + secondBuster;
        }

        System.out.println(sum);
    } main {
        // write your code here
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int[] a = new int[n + 1];

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

        long sum = 0;

        for (int i = 0; i < n; i++) {
            int b = sc.nextInt();
            int buster = Math.min(a[i], b);
            int secondBuster = Math.min(a[i + 1], b - buster);
            a[i + 1] -= secondBuster;
            sum += buster + secondBuster;
        }

        System.out.println(sum);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] a = new int[n + 1]; a new int[n + 1] n + 1 n 1 for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        } int i = 0; int i = 0; i 0 i < n + 1 i n + 1 n 1 i++ i++ i {
            a[i] = sc.nextInt();
        } {
            a[i] = sc.nextInt();
        } a[i] = sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc long sum = 0; sum 0 for (int i = 0; i < n; i++) {
            int b = sc.nextInt();
            int buster = Math.min(a[i], b);
            int secondBuster = Math.min(a[i + 1], b - buster);
            a[i + 1] -= secondBuster;
            sum += buster + secondBuster;
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            int b = sc.nextInt();
            int buster = Math.min(a[i], b);
            int secondBuster = Math.min(a[i + 1], b - buster);
            a[i + 1] -= secondBuster;
            sum += buster + secondBuster;
        } {
            int b = sc.nextInt();
            int buster = Math.min(a[i], b);
            int secondBuster = Math.min(a[i + 1], b - buster);
            a[i + 1] -= secondBuster;
            sum += buster + secondBuster;
        } int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc int buster = Math.min(a[i], b); buster Math.min(a[i], b) Math.min Math a[i] a i b int secondBuster = Math.min(a[i + 1], b - buster); secondBuster Math.min(a[i + 1], b - buster) Math.min Math a[i + 1] a i + 1 i 1 b - buster b buster a[i + 1] -= secondBuster a[i + 1] a i + 1 i 1 secondBuster sum += buster + secondBuster sum buster + secondBuster buster secondBuster System.out.println(sum) System.out.println System.out System System.out sum String[] args args public class Main {

    public static void main(String[] args) {
        // write your code here
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int[] a = new int[n + 1];

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

        long sum = 0;

        for (int i = 0; i < n; i++) {
            int b = sc.nextInt();
            int buster = Math.min(a[i], b);
            int secondBuster = Math.min(a[i + 1], b - buster);
            a[i + 1] -= secondBuster;
            sum += buster + secondBuster;
        }

        System.out.println(sum);
    }
} public class Main {

    public static void main(String[] args) {
        // write your code here
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int[] a = new int[n + 1];

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

        long sum = 0;

        for (int i = 0; i < n; i++) {
            int b = sc.nextInt();
            int buster = Math.min(a[i], b);
            int secondBuster = Math.min(a[i + 1], b - buster);
            a[i + 1] -= secondBuster;
            sum += buster + secondBuster;
        }

        System.out.println(sum);
    }
} Main
import java.util.*;

public class Main {

    public static void main(String[] args) {
        // write your code here
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int[] a = new int[n + 1];

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

        long sum = 0;

        for (int i = 0; i < n; i++) {
            int b = sc.nextInt();
            int buster = Math.min(a[i], b);
            int secondBuster = Math.min(a[i + 1], b - buster);
            a[i + 1] -= secondBuster;
            sum += buster + secondBuster;
        }

        System.out.println(sum);
    }
}
