#include <bits/stdc++.h>
using namespace std;
inline long long small(char a, char b) {
  return min(abs(a - b), min(a + 26 - b, b + 26 - a));
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n, pos;
  cin >> n >> pos;
  string x;
  cin >> x;
  bool gotomid = 0;
  int mid = n / 2;
  if (pos > mid) {
    pos = n - pos + 1;
  }
  long long res = small(x[pos - 1], x[n - pos]);
  int right = -1, left = 1e5;
  for (int i = mid - 1; i >= pos; i--)
    if (x[i] != x[n - 1 - i]) {
      right = i;
      break;
    }
  for (int i = 0; i < pos - 1; i++)
    if (x[i] != x[n - 1 - i]) {
      left = i;
      break;
    }
  if (left == 1e5 && right == -1)
    cout << res;
  else if (left != 1e5 && right == -1) {
    for (int i = left; i < pos - 1; i++)
      if (x[i] != x[n - 1 - i]) res += small(x[i], x[n - 1 - i]);
    res += pos - 1 - left;
    cout << res;
  } else if (left == 1e5 && right != -1) {
    for (int i = right; i >= pos; i--)
      if (x[i] != x[n - 1 - i]) res += small(x[i], x[n - 1 - i]);
    res += right - (pos - 1);
    cout << res;
  } else {
    for (int i = left; i < pos - 1; i++)
      if (x[i] != x[n - 1 - i]) res += small(x[i], x[n - 1 - i]);
    for (int i = right; i >= pos; i--)
      if (x[i] != x[n - 1 - i]) res += small(x[i], x[n - 1 - i]);
    res += 2 * min(pos - 1 - left, right - (pos - 1)) +
           max(pos - 1 - left, right - (pos - 1));
    cout << res;
  }
}
