import java.util.*;

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 <= n; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        long sum = 0;
        for (int i = 0; i < n; i++) {
            int left = Math.min(a[i], b[i]);
            sum += left;
            a[i] -= left;
            b[i] -= left;
            int right = Math.min(a[i + 1], b[i]);
            sum += right;
            a[i + 1] -= right;
            b[i] -= right;
        }
        System.out.println(sum);
    }
} import java.util.*; util.* java 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 <= n; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        long sum = 0;
        for (int i = 0; i < n; i++) {
            int left = Math.min(a[i], b[i]);
            sum += left;
            a[i] -= left;
            b[i] -= left;
            int right = Math.min(a[i + 1], b[i]);
            sum += right;
            a[i + 1] -= right;
            b[i] -= right;
        }
        System.out.println(sum);
    }
} 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 <= n; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        long sum = 0;
        for (int i = 0; i < n; i++) {
            int left = Math.min(a[i], b[i]);
            sum += left;
            a[i] -= left;
            b[i] -= left;
            int right = Math.min(a[i + 1], b[i]);
            sum += right;
            a[i + 1] -= right;
            b[i] -= right;
        }
        System.out.println(sum);
    } main {
        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 <= n; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        long sum = 0;
        for (int i = 0; i < n; i++) {
            int left = Math.min(a[i], b[i]);
            sum += left;
            a[i] -= left;
            b[i] -= left;
            int right = Math.min(a[i + 1], b[i]);
            sum += right;
            a[i + 1] -= right;
            b[i] -= right;
        }
        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 int[] b = new int[n]; b new int[n] n for (int i = 0; i <= n; i++) {
            a[i] = sc.nextInt();
        } int i = 0; int i = 0; i 0 i <= n i n 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 sum = 0; sum 0 for (int i = 0; i < n; i++) {
            int left = Math.min(a[i], b[i]);
            sum += left;
            a[i] -= left;
            b[i] -= left;
            int right = Math.min(a[i + 1], b[i]);
            sum += right;
            a[i + 1] -= right;
            b[i] -= right;
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            int left = Math.min(a[i], b[i]);
            sum += left;
            a[i] -= left;
            b[i] -= left;
            int right = Math.min(a[i + 1], b[i]);
            sum += right;
            a[i + 1] -= right;
            b[i] -= right;
        } {
            int left = Math.min(a[i], b[i]);
            sum += left;
            a[i] -= left;
            b[i] -= left;
            int right = Math.min(a[i + 1], b[i]);
            sum += right;
            a[i + 1] -= right;
            b[i] -= right;
        } int left = Math.min(a[i], b[i]); left Math.min(a[i], b[i]) Math.min Math a[i] a i b[i] b i sum += left sum left a[i] -= left a[i] a i left b[i] -= left b[i] b i left int right = Math.min(a[i + 1], b[i]); right Math.min(a[i + 1], b[i]) Math.min Math a[i + 1] a i + 1 i 1 b[i] b i sum += right sum right a[i + 1] -= right a[i + 1] a i + 1 i 1 right b[i] -= right b[i] b i right 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();
        int[] a = new int[n + 1];
        int[] b = new int[n];
        for (int i = 0; i <= n; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        long sum = 0;
        for (int i = 0; i < n; i++) {
            int left = Math.min(a[i], b[i]);
            sum += left;
            a[i] -= left;
            b[i] -= left;
            int right = Math.min(a[i + 1], b[i]);
            sum += right;
            a[i + 1] -= right;
            b[i] -= right;
        }
        System.out.println(sum);
    }
} 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 <= n; i++) {
            a[i] = sc.nextInt();
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        long sum = 0;
        for (int i = 0; i < n; i++) {
            int left = Math.min(a[i], b[i]);
            sum += left;
            a[i] -= left;
            b[i] -= left;
            int right = Math.min(a[i + 1], b[i]);
            sum += right;
            a[i + 1] -= right;
            b[i] -= right;
        }
        System.out.println(sum);
    }
} Main
import java.util.*;

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