using System;
using System.IO;

namespace Sandbox
{
    internal class ProgramC
    {
        private static void Main(string[] args)
        {
            var scanner = new Scanner();
            var n = scanner.GetNextAsInt();
            var a1 = scanner.ToIntArrayFromNextLine();
            var b1 = scanner.ToIntArrayFromNextLine();

            long count = 0;

            while (true)
            {
                var countPre = count;

                for (var i = n - 1; i >= 0; i--)
                {
                    var num = Math.Min(a1[i + 1], b1[i]);
                    a1[i + 1] -= num;
                    b1[i] -= num;
                    count += num;

                    num = Math.Min(a1[i], b1[i]);
                    a1[i] -= num;
                    b1[i] -= num;
                    count += num;
                }

                for (var i = 0; i < n; i++)
                {
                    var num = Math.Min(a1[i], b1[i]);
                    a1[i] -= num;
                    b1[i] -= num;
                    count += num;

                    num = Math.Min(a1[i + 1], b1[i]);
                    a1[i + 1] -= num;
                    b1[i] -= num;
                    count += num;
                }

                if (countPre == count)
                {
                    break;
                }
            }

            Console.WriteLine(count);
        }

        #region String Scanner

        public class Scanner
        {
            private const char Separator = ' ';
            private readonly StreamReader _Stream = new StreamReader(Console.OpenStandardInput());
            private int _Pos;
            private string[] _Line = new string[0];

            #region get a element

            public string GetNext()
            {
                // ReSharper disable once InvertIf
                if (this._Pos >= this._Line.Length)
                {
                    // ReSharper disable once PossibleNullReferenceException
                    this._Line = this._Stream.ReadLine().Split(Separator);
                    this._Pos = 0;
                }

                return this._Line[this._Pos++];
            }

            public int GetNextAsInt()
            {
                return int.Parse(this.GetNext());
            }

            public long GetNextAsLong()
            {
                return long.Parse(this.GetNext());
            }

            public double GetNextAsDouble()
            {
                return double.Parse(this.GetNext());
            }

            #endregion

            #region get array

            public string[] ToArrayFromNextLine()
            {
                if (this._Pos >= this._Line.Length)
                {
                    // ReSharper disable once PossibleNullReferenceException
                    this._Line = this._Stream.ReadLine().Split(Separator);
                }

                this._Pos = this._Line.Length;
                return this._Line;
            }

            public int[] ToIntArrayFromNextLine()
            {
                return ToIntArray(this.ToArrayFromNextLine());
            }

            public long[] ToLongArrayFromNextLine()
            {
                return ToLongArray(this.ToArrayFromNextLine());
            }

            public double[] ToDoubleArrayFromNextLine()
            {
                return ToDoubleArray(this.ToArrayFromNextLine());
            }

            #endregion

            #region convert array

            private static int[] ToIntArray(string[] array)
            {
                var result = new int[array.Length];
                for (var i = 0; i < array.Length; i++)
                {
                    result[i] = int.Parse(array[i]);
                }

                return result;
            }

            private static long[] ToLongArray(string[] array)
            {
                var result = new long[array.Length];
                for (var i = 0; i < array.Length; i++)
                {
                    result[i] = long.Parse(array[i]);
                }

                return result;
            }

            private static double[] ToDoubleArray(string[] array)
            {
                var result = new double[array.Length];
                for (var i = 0; i < array.Length; i++)
                {
                    result[i] = double.Parse(array[i]);
                }

                return result;
            }

            #endregion
        }

        #endregion
    }
}


Measured memory_bytes: 30952