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

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];

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

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

    long ans = 0;

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

    System.out.println(ans);

  }

} import java.util.*; util.* java import java.math.*; math.* java 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];

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

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

    long ans = 0;

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

    System.out.println(ans);

  }

} 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];

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

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

    long ans = 0;

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

    System.out.println(ans);

  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    long[] a = new long[n+1];
    long[] b = new long[n];

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

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

    long ans = 0;

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

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

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

    long ans = 0;

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

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

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

    long ans = 0;

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

    System.out.println(ans);

  }

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

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];

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

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

    long ans = 0;

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

    System.out.println(ans);

  }

}
