#include <iostream>
using namespace std;
int main()
{
   
   int n;
   cin >> n;
   int arr[n];

   for ( int i = 0 ; i < n ; i ++ )
   {
      cin >> arr[i];
   }

   int shot = 0;
   int j = n - 1;
   for ( int i = 0 ; i < n / 2 ; i ++ )
   {
      if ( arr[i] > arr[j] )
      {
         shot = shot + ( arr[i] - arr[j] );
      }

      else if ( arr[i] < arr[j] )
      {
         shot = shot + ( arr[j] - arr[i] );
      }

      j --;
   }

   cout << shot;

   return 0;
}