#include <iostream>
using namespace std;
typedef long long ll;
#define REP(i, n)           for(int(i)=0;(i)<(n);++(i))
int dp[1010];
int main(){
    int N; cin >> N;
    REP(i,N){
        int K; cin >> K;
        dp[i+1] = max(dp[i+1], (i-1>=0?dp[i-1]:0)+K);
        dp[i+1] = max(dp[i+1], dp[i]);
    }
    cout << dp[N] << endl;
    return 0;
}