
import java.util.Scanner;

/**
 *
 * @author cs18097
 */
public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        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+1;i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0;i < n;i++){
            b[i] = sc.nextInt();
        }
        for(int i = 0;i< n;i++){
            if(a[i] < b[i]){
                ans += a[i];
                b[i] -= a[i];
                if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                }
            } else {
                ans += b[i];
            }
        }
        System.out.print(ans);
    }
    
} import java.util.Scanner; Scanner java.util public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        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+1;i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0;i < n;i++){
            b[i] = sc.nextInt();
        }
        for(int i = 0;i< n;i++){
            if(a[i] < b[i]){
                ans += a[i];
                b[i] -= a[i];
                if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                }
            } else {
                ans += b[i];
            }
        }
        System.out.print(ans);
    }
    
} Main /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        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+1;i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0;i < n;i++){
            b[i] = sc.nextInt();
        }
        for(int i = 0;i< n;i++){
            if(a[i] < b[i]){
                ans += a[i];
                b[i] -= a[i];
                if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                }
            } else {
                ans += b[i];
            }
        }
        System.out.print(ans);
    } main {
        // TODO code application logic here
        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+1;i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0;i < n;i++){
            b[i] = sc.nextInt();
        }
        for(int i = 0;i< n;i++){
            if(a[i] < b[i]){
                ans += a[i];
                b[i] -= a[i];
                if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                }
            } else {
                ans += b[i];
            }
        }
        System.out.print(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+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 for(int i = 0;i< n;i++){
            if(a[i] < b[i]){
                ans += a[i];
                b[i] -= a[i];
                if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                }
            } else {
                ans += b[i];
            }
        } int i = 0; int i = 0; i 0 i< n i n i++ i++ i {
            if(a[i] < b[i]){
                ans += a[i];
                b[i] -= a[i];
                if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                }
            } else {
                ans += b[i];
            }
        } {
            if(a[i] < b[i]){
                ans += a[i];
                b[i] -= a[i];
                if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                }
            } else {
                ans += b[i];
            }
        } if(a[i] < b[i]){
                ans += a[i];
                b[i] -= a[i];
                if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                }
            } else {
                ans += b[i];
            } a[i] < b[i] a[i] a i b[i] b i {
                ans += a[i];
                b[i] -= a[i];
                if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                }
            } ans += a[i] ans a[i] a i b[i] -= a[i] b[i] b i a[i] a i if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                } a[i+1]<b[i] a[i+1] a i+1 i 1 b[i] b i {
                    ans += a[i+1];
                    a[i+1]=0;
                } ans += a[i+1] ans a[i+1] a i+1 i 1 a[i+1]=0 a[i+1] a i+1 i 1 0 {
                    ans += b[i];
                    a[i+1] -= b[i];
                } ans += b[i] ans b[i] b i a[i+1] -= b[i] a[i+1] a i+1 i 1 b[i] b i {
                ans += b[i];
            } ans += b[i] ans b[i] b i System.out.print(ans) System.out.print System.out System System.out ans String[] args args public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        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+1;i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0;i < n;i++){
            b[i] = sc.nextInt();
        }
        for(int i = 0;i< n;i++){
            if(a[i] < b[i]){
                ans += a[i];
                b[i] -= a[i];
                if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                }
            } else {
                ans += b[i];
            }
        }
        System.out.print(ans);
    }
    
} public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        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+1;i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0;i < n;i++){
            b[i] = sc.nextInt();
        }
        for(int i = 0;i< n;i++){
            if(a[i] < b[i]){
                ans += a[i];
                b[i] -= a[i];
                if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                }
            } else {
                ans += b[i];
            }
        }
        System.out.print(ans);
    }
    
} Main

import java.util.Scanner;

/**
 *
 * @author cs18097
 */
public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        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+1;i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0;i < n;i++){
            b[i] = sc.nextInt();
        }
        for(int i = 0;i< n;i++){
            if(a[i] < b[i]){
                ans += a[i];
                b[i] -= a[i];
                if(a[i+1]<b[i]){
                    ans += a[i+1];
                    a[i+1]=0;
                }else{
                    ans += b[i];
                    a[i+1] -= b[i];
                }
            } else {
                ans += b[i];
            }
        }
        System.out.print(ans);
    }
    
}
