import java.util.Scanner;

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];
        int[] b = new int[n];
        long counter = 0;
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
            counter += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        sc.close();

        // 倒す処理
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                a[i] -= b[i];
            } else {
                a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i]));
                a[i] = 0;
            }
        }

        // 回答
        long ans = counter;
        for (int i = 0; i < n + 1; i++) {
            ans -= a[i];
        }
        System.out.println(ans);
    }

} import java.util.Scanner; Scanner 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];
        int[] b = new int[n];
        long counter = 0;
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
            counter += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        sc.close();

        // 倒す処理
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                a[i] -= b[i];
            } else {
                a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i]));
                a[i] = 0;
            }
        }

        // 回答
        long ans = counter;
        for (int i = 0; i < n + 1; i++) {
            ans -= a[i];
        }
        System.out.println(ans);
    }

} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n + 1];
        int[] b = new int[n];
        long counter = 0;
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
            counter += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        sc.close();

        // 倒す処理
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                a[i] -= b[i];
            } else {
                a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i]));
                a[i] = 0;
            }
        }

        // 回答
        long ans = counter;
        for (int i = 0; i < n + 1; i++) {
            ans -= a[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];
        long counter = 0;
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
            counter += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        sc.close();

        // 倒す処理
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                a[i] -= b[i];
            } else {
                a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i]));
                a[i] = 0;
            }
        }

        // 回答
        long ans = counter;
        for (int i = 0; i < n + 1; i++) {
            ans -= a[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 long counter = 0; counter 0 for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
            counter += a[i];
        } int i = 0; int i = 0; i 0 i < n + 1 i n + 1 n 1 i++ i++ i {
            a[i] = sc.nextInt();
            counter += a[i];
        } {
            a[i] = sc.nextInt();
            counter += a[i];
        } a[i] = sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc counter += a[i] counter a[i] a i 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 sc.close() sc.close sc for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                a[i] -= b[i];
            } else {
                a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i]));
                a[i] = 0;
            }
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            if (a[i] >= b[i]) {
                a[i] -= b[i];
            } else {
                a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i]));
                a[i] = 0;
            }
        } {
            if (a[i] >= b[i]) {
                a[i] -= b[i];
            } else {
                a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i]));
                a[i] = 0;
            }
        } if (a[i] >= b[i]) {
                a[i] -= b[i];
            } else {
                a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i]));
                a[i] = 0;
            } a[i] >= b[i] a[i] a i b[i] b i {
                a[i] -= b[i];
            } a[i] -= b[i] a[i] a i b[i] b i {
                a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i]));
                a[i] = 0;
            } a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i])) a[i + 1] a i + 1 i 1 Math.max(0, a[i + 1] - (b[i] - a[i])) Math.max Math 0 a[i + 1] - (b[i] - a[i]) a[i + 1] a i + 1 i 1 (b[i] - a[i]) b[i] b i a[i] a i a[i] = 0 a[i] a i 0 long ans = counter; ans counter for (int i = 0; i < n + 1; i++) {
            ans -= a[i];
        } int i = 0; int i = 0; i 0 i < n + 1 i n + 1 n 1 i++ i++ i {
            ans -= a[i];
        } {
            ans -= a[i];
        } ans -= a[i] ans a[i] a 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();
        int[] a = new int[n + 1];
        int[] b = new int[n];
        long counter = 0;
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
            counter += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        sc.close();

        // 倒す処理
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                a[i] -= b[i];
            } else {
                a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i]));
                a[i] = 0;
            }
        }

        // 回答
        long ans = counter;
        for (int i = 0; i < n + 1; i++) {
            ans -= a[i];
        }
        System.out.println(ans);
    }

} 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];
        int[] b = new int[n];
        long counter = 0;
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
            counter += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        sc.close();

        // 倒す処理
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                a[i] -= b[i];
            } else {
                a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i]));
                a[i] = 0;
            }
        }

        // 回答
        long ans = counter;
        for (int i = 0; i < n + 1; i++) {
            ans -= a[i];
        }
        System.out.println(ans);
    }

} Main
import java.util.Scanner;

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];
        int[] b = new int[n];
        long counter = 0;
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
            counter += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        sc.close();

        // 倒す処理
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                a[i] -= b[i];
            } else {
                a[i + 1] = Math.max(0, a[i + 1] - (b[i] - a[i]));
                a[i] = 0;
            }
        }

        // 回答
        long ans = counter;
        for (int i = 0; i < n + 1; i++) {
            ans -= a[i];
        }
        System.out.println(ans);
    }

}
