import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        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+1; i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0; i < n; i++){
            b[i] = sc.nextInt();
        }
        long ans = 0;
        for(int i = 0; i < n; i++){
            if(a[i] <= b[i]){
                ans += a[i];
                b[i] -= a[i];
                a[i] = 0;
                ans += Math.min(a[i+1], b[i]);
                a[i+1] = Math.max(0,a[i+1]-b[i]);
            }else{
                ans += b[i];
            }
        }
        System.out.println(ans);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        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+1; i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0; i < n; i++){
            b[i] = sc.nextInt();
        }
        long ans = 0;
        for(int i = 0; i < n; i++){
            if(a[i] <= b[i]){
                ans += a[i];
                b[i] -= a[i];
                a[i] = 0;
                ans += Math.min(a[i+1], b[i]);
                a[i+1] = Math.max(0,a[i+1]-b[i]);
            }else{
                ans += b[i];
            }
        }
        System.out.println(ans);
    }
} Main public static void main(String[] args) throws Exception {
        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+1; i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0; i < n; i++){
            b[i] = sc.nextInt();
        }
        long ans = 0;
        for(int i = 0; i < n; i++){
            if(a[i] <= b[i]){
                ans += a[i];
                b[i] -= a[i];
                a[i] = 0;
                ans += Math.min(a[i+1], b[i]);
                a[i+1] = Math.max(0,a[i+1]-b[i]);
            }else{
                ans += b[i];
            }
        }
        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];
        for(int i = 0; i < n+1; i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0; i < n; i++){
            b[i] = sc.nextInt();
        }
        long ans = 0;
        for(int i = 0; i < n; i++){
            if(a[i] <= b[i]){
                ans += a[i];
                b[i] -= a[i];
                a[i] = 0;
                ans += Math.min(a[i+1], b[i]);
                a[i+1] = Math.max(0,a[i+1]-b[i]);
            }else{
                ans += b[i];
            }
        }
        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 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 ans = 0; ans 0 for(int i = 0; i < n; i++){
            if(a[i] <= b[i]){
                ans += a[i];
                b[i] -= a[i];
                a[i] = 0;
                ans += Math.min(a[i+1], b[i]);
                a[i+1] = Math.max(0,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];
                a[i] = 0;
                ans += Math.min(a[i+1], b[i]);
                a[i+1] = Math.max(0,a[i+1]-b[i]);
            }else{
                ans += b[i];
            }
        } {
            if(a[i] <= b[i]){
                ans += a[i];
                b[i] -= a[i];
                a[i] = 0;
                ans += Math.min(a[i+1], b[i]);
                a[i+1] = Math.max(0,a[i+1]-b[i]);
            }else{
                ans += b[i];
            }
        } if(a[i] <= b[i]){
                ans += a[i];
                b[i] -= a[i];
                a[i] = 0;
                ans += Math.min(a[i+1], b[i]);
                a[i+1] = Math.max(0,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];
                a[i] = 0;
                ans += Math.min(a[i+1], b[i]);
                a[i+1] = Math.max(0,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 a[i] = 0 a[i] a i 0 ans += Math.min(a[i+1], b[i]) ans Math.min(a[i+1], b[i]) Math.min Math a[i+1] a i+1 i 1 b[i] b i a[i+1] = Math.max(0,a[i+1]-b[i]) a[i+1] a i+1 i 1 Math.max(0,a[i+1]-b[i]) Math.max Math 0 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.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        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+1; i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0; i < n; i++){
            b[i] = sc.nextInt();
        }
        long ans = 0;
        for(int i = 0; i < n; i++){
            if(a[i] <= b[i]){
                ans += a[i];
                b[i] -= a[i];
                a[i] = 0;
                ans += Math.min(a[i+1], b[i]);
                a[i+1] = Math.max(0,a[i+1]-b[i]);
            }else{
                ans += b[i];
            }
        }
        System.out.println(ans);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        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+1; i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0; i < n; i++){
            b[i] = sc.nextInt();
        }
        long ans = 0;
        for(int i = 0; i < n; i++){
            if(a[i] <= b[i]){
                ans += a[i];
                b[i] -= a[i];
                a[i] = 0;
                ans += Math.min(a[i+1], b[i]);
                a[i+1] = Math.max(0,a[i+1]-b[i]);
            }else{
                ans += b[i];
            }
        }
        System.out.println(ans);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        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+1; i++){
            a[i] = sc.nextInt();
        }
        for(int i = 0; i < n; i++){
            b[i] = sc.nextInt();
        }
        long ans = 0;
        for(int i = 0; i < n; i++){
            if(a[i] <= b[i]){
                ans += a[i];
                b[i] -= a[i];
                a[i] = 0;
                ans += Math.min(a[i+1], b[i]);
                a[i+1] = Math.max(0,a[i+1]-b[i]);
            }else{
                ans += b[i];
            }
        }
        System.out.println(ans);
    }
}