#include <bits/stdc++.h>
using namespace std;
int distance(char a, char b) {
  int d = abs(a - b);
  int d1 = 26 - d;
  return min(d, d1);
}
int main() {
  int n;
  string A;
  int cursor;
  cin >> n >> cursor >> A;
  cursor--;
  n--;
  cursor = min(cursor, n - cursor);
  int middle = n / 2;
  int leftmost = cursor, rightmost = cursor;
  for (int i = cursor; i <= middle; i++)
    if (A[i] != A[n - i]) rightmost = i;
  for (int i = cursor; i >= 0; i--)
    if (A[i] != A[n - i]) leftmost = i;
  int vertical_moves = 0;
  for (int i = leftmost; i <= rightmost; i++)
    vertical_moves += min(abs(A[i] - A[n - i]), 26 - abs(A[i] - A[n - i]));
  int horizontal_moves = min((cursor - leftmost) + (rightmost - leftmost),
                             (rightmost - cursor) + (rightmost - leftmost));
  int total_moves = horizontal_moves + vertical_moves;
  cout << total_moves;
  return 0;
}
