#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
//-------------------------------------------------------

int N;
ll A[202020];

ll dp[202020][2][3];

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N;
	
	FOR(i,N+1) FOR(x,2) FOR(y,3) dp[i][x][y]=-1LL<<60;
	dp[0][1][0]=0;
	
	FOR(i,N) {
		cin>>x;
		FOR(j,2) FOR(k,3) {
			// not take
			if(k+j<3) dp[i+1][1][k+j]=max(dp[i+1][1][k+j],dp[i][j][k]);
			// take
			if(j==1) dp[i+1][0][k]=max(dp[i+1][0][k],dp[i][j][k]+x);
		}
	}
	
	if(N%2==0) cout<<max(dp[N][1][0],dp[N][0][1])<<endl;
	else cout<<max(dp[N][0][2],dp[N][1][1])<<endl;
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}
