#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define FOR(i,n) for(int i=0;i<(n);i++)
#define MOD 1000000007
#define all(x) (x).begin(),(x).end()
template<class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}
template<class T> inline T GCD(T a,T b){T c;while(b!=0){c=a%b;a=b;b=c;}return a;}
template<class T> inline T LCM(T a,T b){return a/GCD(a,b)*b;}

int main(){
	int n;
	cin >> n;
	int v[1010];
	FOR(i,n){
		cin >> v[i+1];
	}
	int dp[1010]={0};
	dp[1]=v[1];
	for(int i=2;i<=n;i++){
		dp[i]=max(dp[i-1],dp[i-2]+v[i]);
	}
	cout << dp[n] << endl;
}