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];
        long ans = 0;
        for (int i=0;i<=n;i++)a[i]=sc.nextInt();
        for (int i=0;i<n;i++)b[i]=sc.nextInt();
        for (int i=0;i<n;i++){
            int def1 = a[i];
            int def2 = a[i+1];
            a[i] = Math.max(0,a[i]-b[i]);
            a[i+1] = Math.max(0,Math.min(a[i+1],a[i+1]+def1-b[i]));
            ans+=def1-a[i]+def2-a[i+1];
        }
        System.out.println(ans);

    }
} 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];
        long ans = 0;
        for (int i=0;i<=n;i++)a[i]=sc.nextInt();
        for (int i=0;i<n;i++)b[i]=sc.nextInt();
        for (int i=0;i<n;i++){
            int def1 = a[i];
            int def2 = a[i+1];
            a[i] = Math.max(0,a[i]-b[i]);
            a[i+1] = Math.max(0,Math.min(a[i+1],a[i+1]+def1-b[i]));
            ans+=def1-a[i]+def2-a[i+1];
        }
        System.out.println(ans);

    }
} 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];
        long ans = 0;
        for (int i=0;i<=n;i++)a[i]=sc.nextInt();
        for (int i=0;i<n;i++)b[i]=sc.nextInt();
        for (int i=0;i<n;i++){
            int def1 = a[i];
            int def2 = a[i+1];
            a[i] = Math.max(0,a[i]-b[i]);
            a[i+1] = Math.max(0,Math.min(a[i+1],a[i+1]+def1-b[i]));
            ans+=def1-a[i]+def2-a[i+1];
        }
        System.out.println(ans);

    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n];
        long ans = 0;
        for (int i=0;i<=n;i++)a[i]=sc.nextInt();
        for (int i=0;i<n;i++)b[i]=sc.nextInt();
        for (int i=0;i<n;i++){
            int def1 = a[i];
            int def2 = a[i+1];
            a[i] = Math.max(0,a[i]-b[i]);
            a[i+1] = Math.max(0,Math.min(a[i+1],a[i+1]+def1-b[i]));
            ans+=def1-a[i]+def2-a[i+1];
        }
        System.out.println(ans);

    } 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 long ans = 0; ans 0 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] 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] b i sc.nextInt() sc.nextInt sc for (int i=0;i<n;i++){
            int def1 = a[i];
            int def2 = a[i+1];
            a[i] = Math.max(0,a[i]-b[i]);
            a[i+1] = Math.max(0,Math.min(a[i+1],a[i+1]+def1-b[i]));
            ans+=def1-a[i]+def2-a[i+1];
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
            int def1 = a[i];
            int def2 = a[i+1];
            a[i] = Math.max(0,a[i]-b[i]);
            a[i+1] = Math.max(0,Math.min(a[i+1],a[i+1]+def1-b[i]));
            ans+=def1-a[i]+def2-a[i+1];
        } {
            int def1 = a[i];
            int def2 = a[i+1];
            a[i] = Math.max(0,a[i]-b[i]);
            a[i+1] = Math.max(0,Math.min(a[i+1],a[i+1]+def1-b[i]));
            ans+=def1-a[i]+def2-a[i+1];
        } int def1 = a[i]; def1 a[i] a i int def2 = a[i+1]; def2 a[i+1] a i+1 i 1 a[i] = Math.max(0,a[i]-b[i]) a[i] a i Math.max(0,a[i]-b[i]) Math.max Math 0 a[i]-b[i] a[i] a i b[i] b i a[i+1] = Math.max(0,Math.min(a[i+1],a[i+1]+def1-b[i])) a[i+1] a i+1 i 1 Math.max(0,Math.min(a[i+1],a[i+1]+def1-b[i])) Math.max Math 0 Math.min(a[i+1],a[i+1]+def1-b[i]) Math.min Math a[i+1] a i+1 i 1 a[i+1]+def1-b[i] a[i+1]+def1 a[i+1] a i+1 i 1 def1 b[i] b i ans+=def1-a[i]+def2-a[i+1] ans def1-a[i]+def2-a[i+1] def1-a[i]+def2 def1-a[i] def1 a[i] a i def2 a[i+1] a i+1 i 1 System.out.println(ans) System.out.println System.out System System.out ans 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];
        long ans = 0;
        for (int i=0;i<=n;i++)a[i]=sc.nextInt();
        for (int i=0;i<n;i++)b[i]=sc.nextInt();
        for (int i=0;i<n;i++){
            int def1 = a[i];
            int def2 = a[i+1];
            a[i] = Math.max(0,a[i]-b[i]);
            a[i+1] = Math.max(0,Math.min(a[i+1],a[i+1]+def1-b[i]));
            ans+=def1-a[i]+def2-a[i+1];
        }
        System.out.println(ans);

    }
} 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];
        long ans = 0;
        for (int i=0;i<=n;i++)a[i]=sc.nextInt();
        for (int i=0;i<n;i++)b[i]=sc.nextInt();
        for (int i=0;i<n;i++){
            int def1 = a[i];
            int def2 = a[i+1];
            a[i] = Math.max(0,a[i]-b[i]);
            a[i+1] = Math.max(0,Math.min(a[i+1],a[i+1]+def1-b[i]));
            ans+=def1-a[i]+def2-a[i+1];
        }
        System.out.println(ans);

    }
} 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];
        long ans = 0;
        for (int i=0;i<=n;i++)a[i]=sc.nextInt();
        for (int i=0;i<n;i++)b[i]=sc.nextInt();
        for (int i=0;i<n;i++){
            int def1 = a[i];
            int def2 = a[i+1];
            a[i] = Math.max(0,a[i]-b[i]);
            a[i+1] = Math.max(0,Math.min(a[i+1],a[i+1]+def1-b[i]));
            ans+=def1-a[i]+def2-a[i+1];
        }
        System.out.println(ans);

    }
}
