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];
        for (int i=0; i<n+1; i++) {
            a[i] = sc.nextInt();
        }
        long sum=0;
        for (int i=0; i<n; i++) {
            int b = sc.nextInt();
            if (a[i] > b ) {
                a[i]-=b;
                sum+=b;
            }
            else {
                int c=b-a[i];
                sum+=a[i];
                a[i]=0;
                if (a[i+1] > c ) {
                    a[i+1]-=c;
                    sum+=c;
                }
                else {
                    sum+=a[i+1];
                    a[i+1] = 0;
                }
            }
        }

        System.out.println(sum);
    }
} 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];
        for (int i=0; i<n+1; i++) {
            a[i] = sc.nextInt();
        }
        long sum=0;
        for (int i=0; i<n; i++) {
            int b = sc.nextInt();
            if (a[i] > b ) {
                a[i]-=b;
                sum+=b;
            }
            else {
                int c=b-a[i];
                sum+=a[i];
                a[i]=0;
                if (a[i+1] > c ) {
                    a[i+1]-=c;
                    sum+=c;
                }
                else {
                    sum+=a[i+1];
                    a[i+1] = 0;
                }
            }
        }

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

        System.out.println(sum);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        for (int i=0; i<n+1; i++) {
            a[i] = sc.nextInt();
        }
        long sum=0;
        for (int i=0; i<n; i++) {
            int b = sc.nextInt();
            if (a[i] > b ) {
                a[i]-=b;
                sum+=b;
            }
            else {
                int c=b-a[i];
                sum+=a[i];
                a[i]=0;
                if (a[i+1] > c ) {
                    a[i+1]-=c;
                    sum+=c;
                }
                else {
                    sum+=a[i+1];
                    a[i+1] = 0;
                }
            }
        }

        System.out.println(sum);
    } 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 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 long sum=0; sum 0 for (int i=0; i<n; i++) {
            int b = sc.nextInt();
            if (a[i] > b ) {
                a[i]-=b;
                sum+=b;
            }
            else {
                int c=b-a[i];
                sum+=a[i];
                a[i]=0;
                if (a[i+1] > c ) {
                    a[i+1]-=c;
                    sum+=c;
                }
                else {
                    sum+=a[i+1];
                    a[i+1] = 0;
                }
            }
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
            int b = sc.nextInt();
            if (a[i] > b ) {
                a[i]-=b;
                sum+=b;
            }
            else {
                int c=b-a[i];
                sum+=a[i];
                a[i]=0;
                if (a[i+1] > c ) {
                    a[i+1]-=c;
                    sum+=c;
                }
                else {
                    sum+=a[i+1];
                    a[i+1] = 0;
                }
            }
        } {
            int b = sc.nextInt();
            if (a[i] > b ) {
                a[i]-=b;
                sum+=b;
            }
            else {
                int c=b-a[i];
                sum+=a[i];
                a[i]=0;
                if (a[i+1] > c ) {
                    a[i+1]-=c;
                    sum+=c;
                }
                else {
                    sum+=a[i+1];
                    a[i+1] = 0;
                }
            }
        } int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc if (a[i] > b ) {
                a[i]-=b;
                sum+=b;
            }
            else {
                int c=b-a[i];
                sum+=a[i];
                a[i]=0;
                if (a[i+1] > c ) {
                    a[i+1]-=c;
                    sum+=c;
                }
                else {
                    sum+=a[i+1];
                    a[i+1] = 0;
                }
            } a[i] > b a[i] a i b {
                a[i]-=b;
                sum+=b;
            } a[i]-=b a[i] a i b sum+=b sum b {
                int c=b-a[i];
                sum+=a[i];
                a[i]=0;
                if (a[i+1] > c ) {
                    a[i+1]-=c;
                    sum+=c;
                }
                else {
                    sum+=a[i+1];
                    a[i+1] = 0;
                }
            } int c=b-a[i]; c b-a[i] b a[i] a i sum+=a[i] sum a[i] a i a[i]=0 a[i] a i 0 if (a[i+1] > c ) {
                    a[i+1]-=c;
                    sum+=c;
                }
                else {
                    sum+=a[i+1];
                    a[i+1] = 0;
                } a[i+1] > c a[i+1] a i+1 i 1 c {
                    a[i+1]-=c;
                    sum+=c;
                } a[i+1]-=c a[i+1] a i+1 i 1 c sum+=c sum c {
                    sum+=a[i+1];
                    a[i+1] = 0;
                } sum+=a[i+1] sum a[i+1] a i+1 i 1 a[i+1] = 0 a[i+1] a i+1 i 1 0 System.out.println(sum) System.out.println System.out System System.out sum 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];
        for (int i=0; i<n+1; i++) {
            a[i] = sc.nextInt();
        }
        long sum=0;
        for (int i=0; i<n; i++) {
            int b = sc.nextInt();
            if (a[i] > b ) {
                a[i]-=b;
                sum+=b;
            }
            else {
                int c=b-a[i];
                sum+=a[i];
                a[i]=0;
                if (a[i+1] > c ) {
                    a[i+1]-=c;
                    sum+=c;
                }
                else {
                    sum+=a[i+1];
                    a[i+1] = 0;
                }
            }
        }

        System.out.println(sum);
    }
} 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];
        for (int i=0; i<n+1; i++) {
            a[i] = sc.nextInt();
        }
        long sum=0;
        for (int i=0; i<n; i++) {
            int b = sc.nextInt();
            if (a[i] > b ) {
                a[i]-=b;
                sum+=b;
            }
            else {
                int c=b-a[i];
                sum+=a[i];
                a[i]=0;
                if (a[i+1] > c ) {
                    a[i+1]-=c;
                    sum+=c;
                }
                else {
                    sum+=a[i+1];
                    a[i+1] = 0;
                }
            }
        }

        System.out.println(sum);
    }
} 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];
        for (int i=0; i<n+1; i++) {
            a[i] = sc.nextInt();
        }
        long sum=0;
        for (int i=0; i<n; i++) {
            int b = sc.nextInt();
            if (a[i] > b ) {
                a[i]-=b;
                sum+=b;
            }
            else {
                int c=b-a[i];
                sum+=a[i];
                a[i]=0;
                if (a[i+1] > c ) {
                    a[i+1]-=c;
                    sum+=c;
                }
                else {
                    sum+=a[i+1];
                    a[i+1] = 0;
                }
            }
        }

        System.out.println(sum);
    }
}
