#include <stdio.h>

int sum = 0, n, a[103];

int main()
{
  int i, j, tmp;

  scanf("%d", &n);
  for (i = 0; i < n; i++)
    scanf("%d", &a[i]);
  for (i = 0; i < n; i++)
    for (j = 1; j < n; j++)
      if (a[j - 1] > a[j])
        tmp = a[j], a[j] = a[j - 1], a[j - 1] = tmp;

  for (i = 0; i < (n + 1) / 2; i++)
    sum += (a[i] + 1) / 2;
  printf("%d\n", sum);
  return 0;
}