#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include<iostream>
#include<cstdint>
#include<cstddef>
#include<vector>
#include<algorithm>
//#include<atcoder/all>
//using namespace atcoder;
using namespace std;
using i32 = int_fast32_t;
using i64 = int_fast64_t;
using usize = size_t;
using u32 = uint_fast32_t;
using u64 = uint_fast64_t;
using i128 = __int128_t;
using u128 = __uint128_t;
using ld = long double;
template<typename T>
using vec = vector<T>;
#define rep(i, n) for (i64 i = 0; i < (i64)(n); ++i)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define len(hoge) (i64)((hoge).size())
using P = pair<i64,i64>;
void solve(){
}
int main(){
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    i64 n;
    cin >> n;
    vec<i64> v(n);
    rep(i,n)cin >>v[i];
    vec<vec<i64>> dp(n + 1,vec<i64>(2));
    for(i32 i = 1; i <= n; i++){
        dp[i][0] = max(dp[i - 1][1],dp[i][0]);
        dp[i][1] = max(dp[i][1],dp[i - 1][0] + v[i - 1]);
        dp[i][0] = max(dp[i - 1][0],dp[i][0]);
    }
    cout << max(dp[n][0],dp[n][1]) << endl;
}