import java.util.*;
import java.io.*;

public class Main {
   public static void main(String[] args) throws Exception {
      PrintWriter out = new PrintWriter(System.out);
      FastScanner in = new FastScanner(System.in);
      Hop ob = new Hop();
      ob.solve(in, out);
      out.close();
   }

   static class Hop {

      public void solve(FastScanner in, PrintWriter out) {
      	int n = in.nextInt();
      	int[] a = new int[n + 4];
      	int[][] dp = new int[n + 4][2];
      	String[] s = in.next().split(",");
      	for (int i = 0; i < s.length; ++i) a[i + 1] = Integer.parseInt(s[i]);
      	for (int i = n; i >= 0; --i) {
      		int x = Math.max(a[i+1] + dp[i+1][0], 2*a[i+2] + dp[i+2][0]);
      		x = Math.max(x, 3*a[i+3] + dp[i+3][1]);
      		dp[i][0] = Math.max(dp[i][0], x);

      		int y = Math.max(a[i+1] + dp[i+1][1], 2*a[i+2] + dp[i+2][1]);
      		dp[i][1] = Math.max(dp[i][1], y);
      	}
      	out.println(Math.max(dp[0][0], dp[0][1]));
      }
   }
}

class FastScanner
{
   private InputStream stream;
   private byte[] buf = new byte[1024];
   private int curChar;
   private int numChars;

   public FastScanner(InputStream stream)
   {
      this.stream = stream;
   }

   int read()
   {
      if (numChars == -1)
         throw new InputMismatchException();
      if (curChar >= numChars)
      {
         curChar = 0;
         try
         {
            numChars = stream.read(buf);
         }
         catch (IOException e)
         {
            throw new InputMismatchException();
         }

         if (numChars <= 0)
            return -1;
      }
      return buf[curChar++];
   }

   boolean isSpaceChar(int c)
   {
      return c==' '||c=='\n'||c=='\r'||c=='\t'||c==-1;
   }

   boolean isEndline(int c)
   {
      return c=='\n'||c=='\r'||c==-1;
   }

   int nextInt()
   {
      return Integer.parseInt(next());
   }

   long nextLong()
   {
      return Long.parseLong(next());
   }

   double nextDouble()
   {
      return Double.parseDouble(next());
   }

   String next()
   {
      int c = read();
      while (isSpaceChar(c))
         c = read();
      StringBuilder res = new StringBuilder();
      do
      {
         res.appendCodePoint(c);
         c = read();
      } while(!isSpaceChar(c));
      return res.toString();
   }

   String nextLine()
   {
      int c = read();
      while (isEndline(c))
         c = read();

      StringBuilder res = new StringBuilder();
      do
      {
         res.appendCodePoint(c);
         c = read();
      } while(!isEndline(c));
      return res.toString();
   }
}