import java.math.BigDecimal;
import java.util.*;

public class Main {


    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        sc.nextLine();
        String[] aStr = sc.nextLine().split(" ");
        String[] bStr = sc.nextLine().split(" ");

        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = Long.parseLong(aStr[i]);
        }

        for (int i = 0; i < n; i++) {
            b[i] = Long.parseLong(bStr[i]);
        }


        long ans = 0;

        for (int i = 0; i < n; i++) {
            if (b[i] > a[i]) {
                ans += a[i];
                b[i] -= a[i];
            } else {
                ans += b[i];
                continue;
            }

            if(b[i] > a[i + 1]){
                ans += a[i + 1];
                a[i + 1] = 0;
            } else {
                ans += b[i];
                a[i + 1] -= b[i];
            }

        }

        System.out.println(ans);
    }


} import java.math.BigDecimal; BigDecimal java.math import java.util.*; util.* java public class Main {


    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        sc.nextLine();
        String[] aStr = sc.nextLine().split(" ");
        String[] bStr = sc.nextLine().split(" ");

        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = Long.parseLong(aStr[i]);
        }

        for (int i = 0; i < n; i++) {
            b[i] = Long.parseLong(bStr[i]);
        }


        long ans = 0;

        for (int i = 0; i < n; i++) {
            if (b[i] > a[i]) {
                ans += a[i];
                b[i] -= a[i];
            } else {
                ans += b[i];
                continue;
            }

            if(b[i] > a[i + 1]){
                ans += a[i + 1];
                a[i + 1] = 0;
            } else {
                ans += b[i];
                a[i + 1] -= b[i];
            }

        }

        System.out.println(ans);
    }


} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        sc.nextLine();
        String[] aStr = sc.nextLine().split(" ");
        String[] bStr = sc.nextLine().split(" ");

        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = Long.parseLong(aStr[i]);
        }

        for (int i = 0; i < n; i++) {
            b[i] = Long.parseLong(bStr[i]);
        }


        long ans = 0;

        for (int i = 0; i < n; i++) {
            if (b[i] > a[i]) {
                ans += a[i];
                b[i] -= a[i];
            } else {
                ans += b[i];
                continue;
            }

            if(b[i] > a[i + 1]){
                ans += a[i + 1];
                a[i + 1] = 0;
            } else {
                ans += b[i];
                a[i + 1] -= b[i];
            }

        }

        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        sc.nextLine();
        String[] aStr = sc.nextLine().split(" ");
        String[] bStr = sc.nextLine().split(" ");

        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = Long.parseLong(aStr[i]);
        }

        for (int i = 0; i < n; i++) {
            b[i] = Long.parseLong(bStr[i]);
        }


        long ans = 0;

        for (int i = 0; i < n; i++) {
            if (b[i] > a[i]) {
                ans += a[i];
                b[i] -= a[i];
            } else {
                ans += b[i];
                continue;
            }

            if(b[i] > a[i + 1]){
                ans += a[i + 1];
                a[i + 1] = 0;
            } else {
                ans += b[i];
                a[i + 1] -= 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 sc.nextLine() sc.nextLine sc String[] aStr = sc.nextLine().split(" "); aStr sc.nextLine().split(" ") sc.nextLine().split sc.nextLine() sc.nextLine sc " " String[] bStr = sc.nextLine().split(" "); bStr sc.nextLine().split(" ") sc.nextLine().split sc.nextLine() sc.nextLine 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 + 1; i++) {
            a[i] = Long.parseLong(aStr[i]);
        } int i = 0; int i = 0; i 0 i < n + 1 i n + 1 n 1 i++ i++ i {
            a[i] = Long.parseLong(aStr[i]);
        } {
            a[i] = Long.parseLong(aStr[i]);
        } a[i] = Long.parseLong(aStr[i]) a[i] a i Long.parseLong(aStr[i]) Long.parseLong Long aStr[i] aStr i for (int i = 0; i < n; i++) {
            b[i] = Long.parseLong(bStr[i]);
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            b[i] = Long.parseLong(bStr[i]);
        } {
            b[i] = Long.parseLong(bStr[i]);
        } b[i] = Long.parseLong(bStr[i]) b[i] b i Long.parseLong(bStr[i]) Long.parseLong Long bStr[i] bStr i long ans = 0; ans 0 for (int i = 0; i < n; i++) {
            if (b[i] > a[i]) {
                ans += a[i];
                b[i] -= a[i];
            } else {
                ans += b[i];
                continue;
            }

            if(b[i] > a[i + 1]){
                ans += a[i + 1];
                a[i + 1] = 0;
            } else {
                ans += b[i];
                a[i + 1] -= b[i];
            }

        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            if (b[i] > a[i]) {
                ans += a[i];
                b[i] -= a[i];
            } else {
                ans += b[i];
                continue;
            }

            if(b[i] > a[i + 1]){
                ans += a[i + 1];
                a[i + 1] = 0;
            } else {
                ans += b[i];
                a[i + 1] -= b[i];
            }

        } {
            if (b[i] > a[i]) {
                ans += a[i];
                b[i] -= a[i];
            } else {
                ans += b[i];
                continue;
            }

            if(b[i] > a[i + 1]){
                ans += a[i + 1];
                a[i + 1] = 0;
            } else {
                ans += b[i];
                a[i + 1] -= b[i];
            }

        } if (b[i] > a[i]) {
                ans += a[i];
                b[i] -= a[i];
            } else {
                ans += b[i];
                continue;
            } b[i] > a[i] b[i] b i a[i] a i {
                ans += a[i];
                b[i] -= a[i];
            } ans += a[i] ans a[i] a i b[i] -= a[i] b[i] b i a[i] a i {
                ans += b[i];
                continue;
            } ans += b[i] ans b[i] b i continue; if(b[i] > a[i + 1]){
                ans += a[i + 1];
                a[i + 1] = 0;
            } else {
                ans += b[i];
                a[i + 1] -= b[i];
            } b[i] > a[i + 1] b[i] b i a[i + 1] a i + 1 i 1 {
                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 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) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        sc.nextLine();
        String[] aStr = sc.nextLine().split(" ");
        String[] bStr = sc.nextLine().split(" ");

        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = Long.parseLong(aStr[i]);
        }

        for (int i = 0; i < n; i++) {
            b[i] = Long.parseLong(bStr[i]);
        }


        long ans = 0;

        for (int i = 0; i < n; i++) {
            if (b[i] > a[i]) {
                ans += a[i];
                b[i] -= a[i];
            } else {
                ans += b[i];
                continue;
            }

            if(b[i] > a[i + 1]){
                ans += a[i + 1];
                a[i + 1] = 0;
            } else {
                ans += b[i];
                a[i + 1] -= b[i];
            }

        }

        System.out.println(ans);
    }


} public class Main {


    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        sc.nextLine();
        String[] aStr = sc.nextLine().split(" ");
        String[] bStr = sc.nextLine().split(" ");

        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = Long.parseLong(aStr[i]);
        }

        for (int i = 0; i < n; i++) {
            b[i] = Long.parseLong(bStr[i]);
        }


        long ans = 0;

        for (int i = 0; i < n; i++) {
            if (b[i] > a[i]) {
                ans += a[i];
                b[i] -= a[i];
            } else {
                ans += b[i];
                continue;
            }

            if(b[i] > a[i + 1]){
                ans += a[i + 1];
                a[i + 1] = 0;
            } else {
                ans += b[i];
                a[i + 1] -= b[i];
            }

        }

        System.out.println(ans);
    }


} Main
import java.math.BigDecimal;
import java.util.*;

public class Main {


    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        sc.nextLine();
        String[] aStr = sc.nextLine().split(" ");
        String[] bStr = sc.nextLine().split(" ");

        long[] a = new long[n + 1];
        long[] b = new long[n];
        for (int i = 0; i < n + 1; i++) {
            a[i] = Long.parseLong(aStr[i]);
        }

        for (int i = 0; i < n; i++) {
            b[i] = Long.parseLong(bStr[i]);
        }


        long ans = 0;

        for (int i = 0; i < n; i++) {
            if (b[i] > a[i]) {
                ans += a[i];
                b[i] -= a[i];
            } else {
                ans += b[i];
                continue;
            }

            if(b[i] > a[i + 1]){
                ans += a[i + 1];
                a[i + 1] = 0;
            } else {
                ans += b[i];
                a[i + 1] -= b[i];
            }

        }

        System.out.println(ans);
    }


}
