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 ans2=0;
        for(int i=0;i<=n;i++){
            a[i]=sc.nextInt();
            ans2+=a[i];
        }
        for(int i=0;i<n;i++){
            b[i]=sc.nextInt();
        }
        for(int i=0;i<n;i++){
            int po=Math.max(a[i]-b[i],0);
            b[i]=Math.max(b[i]-a[i],0);
            a[i]=po;
            a[i+1]=Math.max(a[i+1]-b[i],0);
        }
        long ans=0;
        for(int i=0;i<n+1;i++){
            ans+=a[i];
        }
        System.out.println(ans2-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 ans2=0;
        for(int i=0;i<=n;i++){
            a[i]=sc.nextInt();
            ans2+=a[i];
        }
        for(int i=0;i<n;i++){
            b[i]=sc.nextInt();
        }
        for(int i=0;i<n;i++){
            int po=Math.max(a[i]-b[i],0);
            b[i]=Math.max(b[i]-a[i],0);
            a[i]=po;
            a[i+1]=Math.max(a[i+1]-b[i],0);
        }
        long ans=0;
        for(int i=0;i<n+1;i++){
            ans+=a[i];
        }
        System.out.println(ans2-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 ans2=0;
        for(int i=0;i<=n;i++){
            a[i]=sc.nextInt();
            ans2+=a[i];
        }
        for(int i=0;i<n;i++){
            b[i]=sc.nextInt();
        }
        for(int i=0;i<n;i++){
            int po=Math.max(a[i]-b[i],0);
            b[i]=Math.max(b[i]-a[i],0);
            a[i]=po;
            a[i+1]=Math.max(a[i+1]-b[i],0);
        }
        long ans=0;
        for(int i=0;i<n+1;i++){
            ans+=a[i];
        }
        System.out.println(ans2-ans);
    } main {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int []a=new int[n+1];
        int []b=new int[n];
        long ans2=0;
        for(int i=0;i<=n;i++){
            a[i]=sc.nextInt();
            ans2+=a[i];
        }
        for(int i=0;i<n;i++){
            b[i]=sc.nextInt();
        }
        for(int i=0;i<n;i++){
            int po=Math.max(a[i]-b[i],0);
            b[i]=Math.max(b[i]-a[i],0);
            a[i]=po;
            a[i+1]=Math.max(a[i+1]-b[i],0);
        }
        long ans=0;
        for(int i=0;i<n+1;i++){
            ans+=a[i];
        }
        System.out.println(ans2-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 ans2=0; ans2 0 for(int i=0;i<=n;i++){
            a[i]=sc.nextInt();
            ans2+=a[i];
        } int i=0; int i=0; i 0 i<=n i n i++ i++ i {
            a[i]=sc.nextInt();
            ans2+=a[i];
        } {
            a[i]=sc.nextInt();
            ans2+=a[i];
        } a[i]=sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc ans2+=a[i] ans2 a[i] a i 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 for(int i=0;i<n;i++){
            int po=Math.max(a[i]-b[i],0);
            b[i]=Math.max(b[i]-a[i],0);
            a[i]=po;
            a[i+1]=Math.max(a[i+1]-b[i],0);
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
            int po=Math.max(a[i]-b[i],0);
            b[i]=Math.max(b[i]-a[i],0);
            a[i]=po;
            a[i+1]=Math.max(a[i+1]-b[i],0);
        } {
            int po=Math.max(a[i]-b[i],0);
            b[i]=Math.max(b[i]-a[i],0);
            a[i]=po;
            a[i+1]=Math.max(a[i+1]-b[i],0);
        } int po=Math.max(a[i]-b[i],0); po Math.max(a[i]-b[i],0) Math.max Math a[i]-b[i] a[i] a i b[i] b i 0 b[i]=Math.max(b[i]-a[i],0) b[i] b i Math.max(b[i]-a[i],0) Math.max Math b[i]-a[i] b[i] b i a[i] a i 0 a[i]=po a[i] a i po a[i+1]=Math.max(a[i+1]-b[i],0) a[i+1] a i+1 i 1 Math.max(a[i+1]-b[i],0) Math.max Math a[i+1]-b[i] a[i+1] a i+1 i 1 b[i] b i 0 long ans=0; ans 0 for(int i=0;i<n+1;i++){
            ans+=a[i];
        } int i=0; int i=0; i 0 i<n+1 i n+1 n 1 i++ i++ i {
            ans+=a[i];
        } {
            ans+=a[i];
        } ans+=a[i] ans a[i] a i System.out.println(ans2-ans) System.out.println System.out System System.out ans2-ans ans2 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 ans2=0;
        for(int i=0;i<=n;i++){
            a[i]=sc.nextInt();
            ans2+=a[i];
        }
        for(int i=0;i<n;i++){
            b[i]=sc.nextInt();
        }
        for(int i=0;i<n;i++){
            int po=Math.max(a[i]-b[i],0);
            b[i]=Math.max(b[i]-a[i],0);
            a[i]=po;
            a[i+1]=Math.max(a[i+1]-b[i],0);
        }
        long ans=0;
        for(int i=0;i<n+1;i++){
            ans+=a[i];
        }
        System.out.println(ans2-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 ans2=0;
        for(int i=0;i<=n;i++){
            a[i]=sc.nextInt();
            ans2+=a[i];
        }
        for(int i=0;i<n;i++){
            b[i]=sc.nextInt();
        }
        for(int i=0;i<n;i++){
            int po=Math.max(a[i]-b[i],0);
            b[i]=Math.max(b[i]-a[i],0);
            a[i]=po;
            a[i+1]=Math.max(a[i+1]-b[i],0);
        }
        long ans=0;
        for(int i=0;i<n+1;i++){
            ans+=a[i];
        }
        System.out.println(ans2-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 ans2=0;
        for(int i=0;i<=n;i++){
            a[i]=sc.nextInt();
            ans2+=a[i];
        }
        for(int i=0;i<n;i++){
            b[i]=sc.nextInt();
        }
        for(int i=0;i<n;i++){
            int po=Math.max(a[i]-b[i],0);
            b[i]=Math.max(b[i]-a[i],0);
            a[i]=po;
            a[i+1]=Math.max(a[i+1]-b[i],0);
        }
        long ans=0;
        for(int i=0;i<n+1;i++){
            ans+=a[i];
        }
        System.out.println(ans2-ans);
    }
}
