/* package whatever; // don't place package name! */

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

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		int n = 6;
		int[] a = {10, -50, -20, 10, 100, -10, 20}; 

		long[] dp = new long[n + 1];
		long kk = 0;
		
		dp[1] = Math.max(a[1], kk);
		
		dp[2] = Math.max(a[2], dp[1]);
		
		int i = 3;
		while (i <= n) {
			dp[i] = Math.max(a[i] + dp[i - 2], dp[i - 1]);
			i++;
		}
		
		System.out.println(dp[n]);
	
	}
}