#include <bits/stdc++.h>
using namespace std;

const int INF = 0x3f3f3f3f;

signed main(){
  int N; cin >> N;
  vector< int > V( N );
  for( int i = 0; i < N; ++i )
    cin >> V[ i ];
  vector< vector< int > > dp( N + 1, vector< int >( 2, -INF ) );
  dp[ 0 ][ 0 ] = 0;
  for( int i = 0; i < N; ++i )
    dp[ i + 1 ][ 1 ] = max( dp[ i + 1 ][ 1 ], dp[ i ][ 0 ] + V[ i ] ),
    dp[ i + 1 ][ 0 ] = max( { dp[ i + 1 ][ 0 ], dp[ i ][ 0 ], dp[ i ][ 1 ] } );
  cout << max( dp[ N ][ 0 ], dp[ N ][ 1 ] ) << endl;
  return 0;
}