using System;
using System.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace AtCorder
{
    class Program
    {
        static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In, ' '));
        }
        public void Solve(ConsoleInput cin)
        {
            var N = cin.ReadInt;
            var B = cin.ReadIntArray(N - 1);
            var A = new int[N];
            var flag = new bool[N];
            for(int i = 0; i < N; i++)
            {
                A[i] = -1;
                flag[i] = true;
            }
            var ftr = int.MaxValue;
            for(int i = 0; i < N - 1; i++)
            {
                if(B[i] == 0)
                {
                    A[i] = 0;
                    A[i + 1] = 0;
                    flag[i] = false;
                    flag[i + 1] = false;
                    continue;
                }
                if (!flag[i])
                {
                    A[i + 1] = B[i];
                    continue;
                }
                if(flag[i] && A[i] > B[i])
                {
                    A[i] = B[i];
                    A[i + 1] = B[i];
                    flag[i] = false;
                    continue;
                }
                if(A[i] != -1)
                {
                    A[i + 1] = B[i];
                }
                if (A[i] == -1 && flag[i])
                {
                    A[i] = B[i];
                    flag[i] = false;
                    A[i + 1] = B[i];
                }
            }
            var ans = A.Sum();
            WriteLine(ans);
        }

        public long C(long n, long r)
        {
            long[,] Pascal = new long[n + 1, n + 1];
            Pascal[0, 0] = 1;
            for (long i = 1; i <= n; i++)
            {
                Pascal[i, 0] = 1;
                Pascal[i, i] = 1;
                for (long j = 1; j < n; j++)
                {
                    Pascal[i, j] = Pascal[i - 1, j] + Pascal[i - 1, j - 1];
                }
            }
            return Pascal[n, r];
        }

        public class ConsoleInput
        {
            private readonly System.IO.TextReader _stream;
            private char _separator = ' ';
            private Queue<string> inputStream;
            public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
            {
                this._separator = separator;
                this._stream = stream;
                inputStream = new Queue<string>();
            }
            public string Read
            {
                get
                {
                    if (inputStream.Count != 0) return inputStream.Dequeue();
                    string[] tmp = _stream.ReadLine().Split(_separator);
                    for (int i = 0; i < tmp.Length; ++i)
                        inputStream.Enqueue(tmp[i]);
                    return inputStream.Dequeue();
                }
            }
            public string ReadLine { get { return _stream.ReadLine(); } }
            public int ReadInt { get { return int.Parse(Read); } }
            public long ReadLong { get { return long.Parse(Read); } }
            public double ReadDouble { get { return double.Parse(Read); } }
            public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
            public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
            public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
        }
    }
}

Measured memory_bytes: 13396