#include <iostream>
#include <string>
#include <vector>
#define REP(i, n) for(int i = 0; i < (int)(n); i++)
#define FOR(i, j, k) for(int i = (int)(j); i < (int)(k); ++i)
#define print(x) cout << x << endl;
using namespace std;

int main(void){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N;
    
    cin >> N;
    vector<int> V(N);
    REP(i, N) cin >> V[i];
    
    vector<int> dp(N);
    dp[0] = V[0];
    
    if(N != 1) {
        dp[1] = max(V[0], V[1]);
        FOR(i, 2, N){
            dp[i] = max(dp[i-1], dp[i-2] + V[i]);
        }
    }
    print(dp[N-1]);
    return 0;
}