#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) FOR(i,0,n)
#define repr(i,n) for(int i=(n)-1;0<=i;--i)
#define each(e,v) for(auto&& e:(v))
#define all(v) begin(v),end(v)
#define DUMP(x) cerr<<#x<<": "<<(x)<<endl
#define DEBUG(x) cerr<<#x<<": "<<(x)<<" (L"<<__LINE__<<")"<<endl
using namespace std;
using vint = vector<int>;
using vdouble = vector<double>;
using vstring = vector<string>;
using ll = long long;
template <class T> void chmin(T& a, const T& b) { a = min(a, b); }
template <class T> void chmax(T& a, const T& b) { a = max(a, b); }

int main() {
    int n; cin >> n;
    vint v(n);
    rep(i, n) cin >> v[i];
    int dp[1001];
    dp[0] = 0; dp[1] = v[0];
    FOR(i, 2, n+1) {
        dp[i] = max(dp[i-1], dp[i-2] + v[i-1]);
    }
    cout << dp[n] << endl;
    return 0;
}