#include <bits/stdc++.h>   using namespace std;   const long long MAX = 1e6 + 100;   const long long mod = 1e9 + 7;   const long long inf = 1e18 + 12;   vector<long long> arr(MAX);   map<long long, long long> mm;   int main() {     ios_base::sync_with_stdio(false);     cout.tie(NULL);     cout.tie(NULL);     ;     long long tt = 1;     while (tt--) {       long long n;       cin >> n;       long long a[n];       for (long long i = 0; i < n; i++) cin >> a[i];       long long w = 0, b = 0;       long long i = 0;       while (i < n) {         if (i % 2 == 0) {           w += (a[i] + 1) / 2;           b += (a[i]) / 2;         } else {           w += a[i] / 2;           b += (a[i] + 1) / 2;         }         i++;       }       cout << min(w, b);     }   }   