import java.util.Scanner;
/**
* className:test7_2
* Package:PACKAGE_NAME
*
* @Author:swx
* @Create2024/1/1119:57
* @version:1.0
*/
public class test7_2 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int n = scanner.nextInt();
int res = 0;
int[] arr = new int[n];
for (int i = 0; i < n; i++) {
arr[i] = scanner.nextInt();
}
for (int i=n-1; i>=0; i--) {
/*当H>E时, E' = E-(H-E) = 2E-H
当H<E时, E' = E+(E-H) = 2E-H
所以,不管那个数答,最后的能量都是2E-H
那么 E = (E'+H)/2
最后一部假设能量正好为0
* */
int temp = res + arr[i]; //(E'+H)
if (temp % 2 == 0) {
res = temp / 2; // (E'+H)/2
} else {
res = temp / 2 + 1; // 向上取整
}
}
System.out.println(res);
}
}