import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long fii1 = 0;
        long sum = 0;
        for (int i = 0; i < n; i++) {
            long fii = Math.min(a[i] - fii1, b[i]);
            fii1 = Math.min(a[i + 1], b[i] - fii);
            sum += fii + fii1;
        }
        System.out.println(sum);
    }

}
 import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long fii1 = 0;
        long sum = 0;
        for (int i = 0; i < n; i++) {
            long fii = Math.min(a[i] - fii1, b[i]);
            fii1 = Math.min(a[i + 1], b[i] - fii);
            sum += fii + fii1;
        }
        System.out.println(sum);
    }

} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long fii1 = 0;
        long sum = 0;
        for (int i = 0; i < n; i++) {
            long fii = Math.min(a[i] - fii1, b[i]);
            fii1 = Math.min(a[i + 1], b[i] - fii);
            sum += fii + fii1;
        }
        System.out.println(sum);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long fii1 = 0;
        long sum = 0;
        for (int i = 0; i < n; i++) {
            long fii = Math.min(a[i] - fii1, b[i]);
            fii1 = Math.min(a[i + 1], b[i] - fii);
            sum += fii + fii1;
        }
        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 long[] a = new long[n + 1]; a new long[n + 1] n + 1 n 1 long[] b = new long[n]; b new long[n] n 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 for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            b[i] = sc.nextInt();
        } {
            b[i] = sc.nextInt();
        } b[i] = sc.nextInt() b[i] b i sc.nextInt() sc.nextInt sc long fii1 = 0; fii1 0 long sum = 0; sum 0 for (int i = 0; i < n; i++) {
            long fii = Math.min(a[i] - fii1, b[i]);
            fii1 = Math.min(a[i + 1], b[i] - fii);
            sum += fii + fii1;
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            long fii = Math.min(a[i] - fii1, b[i]);
            fii1 = Math.min(a[i + 1], b[i] - fii);
            sum += fii + fii1;
        } {
            long fii = Math.min(a[i] - fii1, b[i]);
            fii1 = Math.min(a[i + 1], b[i] - fii);
            sum += fii + fii1;
        } long fii = Math.min(a[i] - fii1, b[i]); fii Math.min(a[i] - fii1, b[i]) Math.min Math a[i] - fii1 a[i] a i fii1 b[i] b i fii1 = Math.min(a[i + 1], b[i] - fii) fii1 Math.min(a[i + 1], b[i] - fii) Math.min Math a[i + 1] a i + 1 i 1 b[i] - fii b[i] b i fii sum += fii + fii1 sum fii + fii1 fii fii1 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) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long fii1 = 0;
        long sum = 0;
        for (int i = 0; i < n; i++) {
            long fii = Math.min(a[i] - fii1, b[i]);
            fii1 = Math.min(a[i + 1], b[i] - fii);
            sum += fii + fii1;
        }
        System.out.println(sum);
    }

} public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long fii1 = 0;
        long sum = 0;
        for (int i = 0; i < n; i++) {
            long fii = Math.min(a[i] - fii1, b[i]);
            fii1 = Math.min(a[i + 1], b[i] - fii);
            sum += fii + fii1;
        }
        System.out.println(sum);
    }

} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long fii1 = 0;
        long sum = 0;
        for (int i = 0; i < n; i++) {
            long fii = Math.min(a[i] - fii1, b[i]);
            fii1 = Math.min(a[i + 1], b[i] - fii);
            sum += fii + fii1;
        }
        System.out.println(sum);
    }

}

