#include <bits/stdc++.h>
using namespace std;
#define ff              first
#define ss              second
#define pb(x)           push_back(x)
#define mp              make_pair
#define sz(x)           x.size()
#define mem(x ,y)       memset(x , y , sizeof x )
#define all(a )         a.begin() , a.end()
#define endl            "\n"
#define pii             pair<int,int> 
#define clr(x)          x.clear()
#define sl(x )          scanf("%I64d" ,&x)
#define si(x )          scanf("%d" ,&x)
#define forn(i ,x,n )   for(int i = x ; i <= n ; i++ )
#define ford(i ,x,n )   for(int i = x ; i >= n ; i-- )
#define rep(i,n )       for(int i= 0; i<n ; i++ )
#define repi(i,n )      for(int i= 1; i<=n ; i++ )
#define repit(i, c)     for( __typeof((c).begin()) i = (c).begin(); i != (c).end();++i )
#define dbg(args...)    do {   cerr << #args << ' ' ;  print(args); } while(0); cerr<< endl ;
typedef long long ll  ;
ll mod =  1e9+7, mod2 = 998244353 ; 
typedef unsigned long long  ull ;
int setbit(int n, int pos  ) { return n = n|(1<< pos) ; }
int resetbit(int n,int pos ) {  return n =  n & ~(1<<pos ); }
bool checkbit(int  n,int pos ) { return (bool ) (n&(1<<pos))  ; }
template< typename T > T mul(T x, T y, T mod = mod ) { x %= mod ; y %= mod ; return (x*y)%mod  ;  }
template< typename T > T add(T x, T y, T mod = mod ) { x %= mod ; y %= mod ; return (x+y)%mod ;  }
template< typename T > T sub(T x, T y, T mod = mod ) { x %= mod ; y %= mod ; return ((x-y)%mod+mod )%mod;  }
template< typename T > T ext_gcd(T num1 , T num2, T &X , T &Y ) { T r2,r1, q2, q1 , x2, x1, y2 ,y1 , x,  y, r   ; x2 = 1; y2 = 0;  x1 = 0; y1 = 1; for( r2 =num1 ,r1 = num2 ;r1 != 0 ; y2 = y1, y1 = y,x2 = x1 ,x1 = x ,r2 = r1, r1 = r) {q1 = r2/r1; x = x2 - q1*x1; y = y2 - q1*y1; r = r2%r1 ; } X = x2 ; Y = y2 ; return r2 ;  }
template< typename T > void print(const T& v) {    cerr << v << ' ' ;}
template< typename T1, typename... T2 > void print( const T1& first, const T2&... rest ){ print(first); print(rest...) ;}
template<class T> string to_str(T t){stringstream ss; ss<<t; return ss.str();} 
template < typename T > 
T  bigmod(T x, T k ,T mod = mod) {
    if(k == 0 ) return (T)1; 
    if(k&1  ) { 
        return ( (x%mod)*bigmod(x,k-1, mod )%mod )%mod ; 
    } else { 
        T ret = bigmod(x,k/2  , mod ) ; 
        ret %= mod ;             
        return (ret*ret )%mod; 
    } 
 
}
template < typename T > 
T  invmod( T x , T m) {  
    return bigmod(x,m-2 , m) ;   
    // long long ret, t ;// 
    // ext_gcd( x, m ,ret ,t  ) ;
    // ret %= m ; if(ret<0) ret += m  ; 
    // return ret;
} 
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
// using namespace __gnu_pbds;
// typedef tree<  int    ,     // change type 
//               null_type, 
//               less_equal  < int  >  ,  // change type ..    
//               rb_tree_tag,
//               tree_order_statistics_node_update> ordered_set;
// debuging ...
template<typename T > 
void dbg_a(T a[] ,int n=10 ) {
    cerr << "[ "; 
        for(int i=0;i <= n ; i++ )
            cerr<<a[i]<<' ' ; 
                cerr<< " ]" <<  endl; 
} 
template < typename F,  typename S >
ostream& operator << ( ostream& os, const pair< F, S > & p ) {
    return os << "[ " << p.first << ", " << p.second << " ]";
}
template < typename T >
ostream &operator << ( ostream & os, const vector< T > &v ) {
    os << "[ "; 
        for(int i=0; i<sz(v) ; i++ )  
            os << v[i] << ' ' ; 
                return os << " ]\n" ; 
} 
template < typename T >
ostream &operator << ( ostream & os, const map< T ,T> &Map  ) {
    os << "[ "; 
        repit(it , Map )    
            os << "[" <<(*it).ff << ' ' << (*it).ss << "] "    ; 
                return os << "]\n" ; 
} 
template < typename T >
ostream &operator << ( ostream & os, const set< T > &Set  ) {
    os << "[ "; 
        repit(it , Set )   
            os <<  *it  << ' ' ; 
                return os << " ]\n" ; 
}  
template < typename T >
ostream &operator << ( ostream & os, const multiset< T > &Set  ) {
    os << "[ "; 
        repit(it , Set )   
            os <<  *it  << ' ' ; 
                return os << " ]\n" ; 
}  
// int dy[] = {-1, +1,0 , 0 };
// int dx[ 10 ] =  {-2,-2, 2, 2  ,+ 1, -1  , +1, -1 }  ;
// int dy[ 10 ] =  {+1,-1, 1, -1 , +2,+2 , -2,-2  }  ;
const int maxn  = (int )1e6+ 123  ;
const ll inf  =  1e18+1223 ;
#define  int  ll  
//////////////////////////////////////////////////////////////
 
int a[maxn ] , cnt[maxn  ]   ,dp[maxn ] , pre[maxn ];  
void solve()  {    
    int  n,  m , x,y , k, ans= 0 , sum = 0  ,  l,r     ;
    cin >> n  ;  
    forn(i ,1,n )  cin >> a[i ] ; 
   
    pre[1] = a[1] ;
    forn(i,3,n )  pre[i] += pre[i-2] + a[i ] ; 

    // dp[1] = a[1]  ; 
    // dp[2] = a[2]  ;  

    forn(i, 2,n ) {
        if(i&1) {

        
            dp[i] =  max(dp[i-1]  , dp[i-2] + a[i] ) ; 


        } else {    

            dp[i]  = max( pre[i-1] , dp[i-2]+ a[i] )  ;  
        }

    }

    // dbg_a(dp) ;  
    cout << dp[n ]  ;















    



}       
signed main() {     
   
        // clock_t st = clock() ;
    ios :: sync_with_stdio(false);  cin.tie(0);  
    cout.tie(0) ; 
        // cout << fixed << setprecision(12) ;
    int  c = 0 ,t = 1 ;  
    // cin>>t ; 
    while(t--) { 
        solve()  ;  
    }   
    // cerr << "Execution time : " << (double  )  (clock()-st )/CLOCKS_PER_SEC << endl ;
    // 12m447476  _)___ .//47d7
 
    return 0 ;   
     
}    



// int dp[3005][3005]  ; 
// string s , t  ; 
// int func(int l  ,int r, int curr  )  {
//     if( l>r  ) return  1 ; 

//     int  &ans =   dp[l][r ]  ;

//     if(ans != -1) return  ans ; 

//     ans = 0  ; 
//     if( s[curr ]==t[ l ] or l >= sz(t)  )  ans += func( l+1,r , curr-1  ) ,  ans%=mod ;     
//     if( s[curr]==t[ r ] or r>= sz(t)   )ans  += func(l,r-1  , curr-1 ) , ans%=  mod ;  

//     return  ans ;


// }

// void solve()  {    
//     int  n,  m , x,y , k, ans= 0 , sum = 0   , l, r ,f= 0  , last   ;
    

//     cin >> s >>  t ; 

//     mem(dp , -1)  ;
//     swap(mod  , mod2)  ; 
//     forn(i, sz(t)-1 , sz(s)-1)  {
//         ans +=  func(0, i ,  i  ) ; 
//         ans%= mod ; 
//     }


//     cout << ans  << endl;  
// }       





Measured memory_bytes: 8356