#include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(false);     cin.tie(0), cout.tie(0);     cin.tie(0), cout.tie(0);     ;     long long int a, b, t, n, m, k, i, j, l, sum = 0, sum1 = 0, ans = 0;     vector<long long int> v;     cin >> n;     for (i = 0; i < n; i++) {       cin >> a;       v.push_back(a);       if (i & 1) {         sum1 += a;       } else         sum += a;     }     ans = max(sum1, sum);     for (i = 0; i < n; i++) {       if (i & 1) {         sum1 -= v[i];         sum += v[i];       } else {         sum -= v[i];         sum1 += v[i];       }       ans = max(ans, max(sum, sum1));     }     cout << ans << endl;     return 0;   }   