import java.util.*;

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