import java.util.Scanner;

public class Main {

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

    long[] a = new long[n + 1];
    long[] b = new long[n];

    long res = 0;

    for (int i = 0; i <= n; i++)
      a[i] = sc.nextLong();
    for (int i = 0; i < n; i++) {
      b[i] = sc.nextLong();
      if (b[i] > a[i]) {
        res += a[i];
        long carry = Math.min(a[i + 1], b[i] - a[i]);
        a[i + 1] -= carry;
        res += carry;
      } else
        res += b[i];
    }

    System.out.println(res);
  }
} 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();

    long[] a = new long[n + 1];
    long[] b = new long[n];

    long res = 0;

    for (int i = 0; i <= n; i++)
      a[i] = sc.nextLong();
    for (int i = 0; i < n; i++) {
      b[i] = sc.nextLong();
      if (b[i] > a[i]) {
        res += a[i];
        long carry = Math.min(a[i + 1], b[i] - a[i]);
        a[i + 1] -= carry;
        res += carry;
      } else
        res += b[i];
    }

    System.out.println(res);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();

    long[] a = new long[n + 1];
    long[] b = new long[n];

    long res = 0;

    for (int i = 0; i <= n; i++)
      a[i] = sc.nextLong();
    for (int i = 0; i < n; i++) {
      b[i] = sc.nextLong();
      if (b[i] > a[i]) {
        res += a[i];
        long carry = Math.min(a[i + 1], b[i] - a[i]);
        a[i + 1] -= carry;
        res += carry;
      } else
        res += b[i];
    }

    System.out.println(res);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();

    long[] a = new long[n + 1];
    long[] b = new long[n];

    long res = 0;

    for (int i = 0; i <= n; i++)
      a[i] = sc.nextLong();
    for (int i = 0; i < n; i++) {
      b[i] = sc.nextLong();
      if (b[i] > a[i]) {
        res += a[i];
        long carry = Math.min(a[i + 1], b[i] - a[i]);
        a[i + 1] -= carry;
        res += carry;
      } else
        res += b[i];
    }

    System.out.println(res);
  } 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 long res = 0; res 0 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] a i sc.nextLong() sc.nextLong sc for (int i = 0; i < n; i++) {
      b[i] = sc.nextLong();
      if (b[i] > a[i]) {
        res += a[i];
        long carry = Math.min(a[i + 1], b[i] - a[i]);
        a[i + 1] -= carry;
        res += carry;
      } else
        res += b[i];
    } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
      b[i] = sc.nextLong();
      if (b[i] > a[i]) {
        res += a[i];
        long carry = Math.min(a[i + 1], b[i] - a[i]);
        a[i + 1] -= carry;
        res += carry;
      } else
        res += b[i];
    } {
      b[i] = sc.nextLong();
      if (b[i] > a[i]) {
        res += a[i];
        long carry = Math.min(a[i + 1], b[i] - a[i]);
        a[i + 1] -= carry;
        res += carry;
      } else
        res += b[i];
    } b[i] = sc.nextLong() b[i] b i sc.nextLong() sc.nextLong sc if (b[i] > a[i]) {
        res += a[i];
        long carry = Math.min(a[i + 1], b[i] - a[i]);
        a[i + 1] -= carry;
        res += carry;
      } else
        res += b[i]; b[i] > a[i] b[i] b i a[i] a i {
        res += a[i];
        long carry = Math.min(a[i + 1], b[i] - a[i]);
        a[i + 1] -= carry;
        res += carry;
      } res += a[i] res a[i] a i long carry = Math.min(a[i + 1], b[i] - a[i]); carry Math.min(a[i + 1], b[i] - a[i]) Math.min Math a[i + 1] a i + 1 i 1 b[i] - a[i] b[i] b i a[i] a i a[i + 1] -= carry a[i + 1] a i + 1 i 1 carry res += carry res carry res += b[i] res b[i] b i System.out.println(res) System.out.println System.out System System.out res String[] args args public class Main {

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

    long[] a = new long[n + 1];
    long[] b = new long[n];

    long res = 0;

    for (int i = 0; i <= n; i++)
      a[i] = sc.nextLong();
    for (int i = 0; i < n; i++) {
      b[i] = sc.nextLong();
      if (b[i] > a[i]) {
        res += a[i];
        long carry = Math.min(a[i + 1], b[i] - a[i]);
        a[i + 1] -= carry;
        res += carry;
      } else
        res += b[i];
    }

    System.out.println(res);
  }
} public class Main {

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

    long[] a = new long[n + 1];
    long[] b = new long[n];

    long res = 0;

    for (int i = 0; i <= n; i++)
      a[i] = sc.nextLong();
    for (int i = 0; i < n; i++) {
      b[i] = sc.nextLong();
      if (b[i] > a[i]) {
        res += a[i];
        long carry = Math.min(a[i + 1], b[i] - a[i]);
        a[i + 1] -= carry;
        res += carry;
      } else
        res += b[i];
    }

    System.out.println(res);
  }
} Main
import java.util.Scanner;

public class Main {

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

    long[] a = new long[n + 1];
    long[] b = new long[n];

    long res = 0;

    for (int i = 0; i <= n; i++)
      a[i] = sc.nextLong();
    for (int i = 0; i < n; i++) {
      b[i] = sc.nextLong();
      if (b[i] > a[i]) {
        res += a[i];
        long carry = Math.min(a[i + 1], b[i] - a[i]);
        a[i + 1] -= carry;
        res += carry;
      } else
        res += b[i];
    }

    System.out.println(res);
  }
}