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 ans = 0;

    for (int i = 0; i <= n; i++) {
      a[i] = sc.nextInt();
    }

    for (int i = 0; i < n; i++) {
      b[i] = sc.nextInt();
    }

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

    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 ans = 0;

    for (int i = 0; i <= n; i++) {
      a[i] = sc.nextInt();
    }

    for (int i = 0; i < n; i++) {
      b[i] = sc.nextInt();
    }

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

    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 ans = 0;

    for (int i = 0; i <= n; i++) {
      a[i] = sc.nextInt();
    }

    for (int i = 0; i < n; i++) {
      b[i] = sc.nextInt();
    }

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

    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 ans = 0;

    for (int i = 0; i <= n; i++) {
      a[i] = sc.nextInt();
    }

    for (int i = 0; i < n; i++) {
      b[i] = sc.nextInt();
    }

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

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

    for (int i = 0; i <= n; i++) {
      a[i] = sc.nextInt();
    }

    for (int i = 0; i < n; i++) {
      b[i] = sc.nextInt();
    }

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

    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 ans = 0;

    for (int i = 0; i <= n; i++) {
      a[i] = sc.nextInt();
    }

    for (int i = 0; i < n; i++) {
      b[i] = sc.nextInt();
    }

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

    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 ans = 0;

    for (int i = 0; i <= n; i++) {
      a[i] = sc.nextInt();
    }

    for (int i = 0; i < n; i++) {
      b[i] = sc.nextInt();
    }

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

    System.out.println(ans);

  }
}