# include <fstream>
 # include <cstring>
 # include <algorithm>
 # include <vector>
 # include <iostream>
 
 # define dim 100005
 
 using namespace std;
 
 ifstream f("oo.in");
 ofstream g("oo.out");
 
 int A[ dim ], dp[ dim ];
 int N, sol = 0;
 
 void citire()
 {
	 int i;
	 f >> N;
	 for ( i = 1 ; i <= N ; i++ )
		 f >> A[ i ];
 }
 void rezolva()
 {
	 int i;
	 //A[ 0 ] = A[ N ];
	 
	 for ( i = 1 ; i < N ; i++ )
		 dp[ i ] = max( dp[ i - 1 ] ,dp[ max( 0, i - 3 ) ] + A[ i ] + A[ i - 1 ] );
	// for ( i = 1 ; i <= N ; i++ )
		// cout << dp[ i ] << " ";
	 
	 if ( sol < dp[ N - 1 ] )
		 sol = dp[ N - 1 ];
 }
 
 int main()
 {
	 citire();
	 rezolva();
	 g << sol;
	 return 0;
 }