#include<iostream>
#include<vector>
#include<set>
#include<map>
#include<list>
#include<stack>
#include<queue>
#include<bitset>
#include<array>
#include<algorithm>
#include<cstdio>
#include<string>
#include<cstdlib>
#define D long long
#define U unsigned
using namespace std;
D n, m,a, b, d, e, x, y, z;
D i, j, k;
char c;
D ma[2];
int main() {
	D t,u;
	cin >> a;
	for (i = 0; i < a; i++) {
		cin >> t;
		u = ma[0];
		ma[0] = max(ma[0],ma[1]);
		ma[1] = u + t;
	}
	cout << max(ma[0], ma[1]) << endl;
}