#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  int n, k;
  cin >> n >> k;
  string ss;
  cin >> ss;
  vector<int> v(n / 2);
  int t = n / 2;
  for (int i = 0; i < n / 2; i++) {
    v[i] = min(abs(ss[i] - ss[n - i - 1]), 26 - abs(ss[i] - ss[n - i - 1]));
  }
  if (k > t) k = n - k + 1;
  k--;
  int ans = 0;
  int s = -1, e = -1;
  for (int i = 0; i < v.size(); i++)
    if (v[i] > 0) {
      s = i;
      break;
    }
  for (int i = v.size() - 1; i >= 0; i--)
    if (v[i] > 0) {
      e = i;
      break;
    }
  if (s == -1 && e == -1) {
    cout << ans;
    return 0;
  } else if (s <= k && e >= k) {
    int t1 = abs(s - k);
    int t2 = abs(e - k);
    if (t1 > t2) {
      for (int i = k; i <= e; i++) ans += v[i];
      ans += 2 * t2;
      for (int i = k - 1; i >= s; i--) ans += v[i];
      ans += t1;
    } else {
      for (int i = k - 1; i >= s; i--) ans += v[i];
      ans += 2 * t1;
      for (int i = k; i <= e; i++) ans += v[i];
      ans += t2;
    }
  } else if (s < k && e < k) {
    int t1 = abs(s - k);
    for (int i = k; i >= s; i--) ans += v[i];
    ans += t1;
  } else if (s > k && e > k) {
    int t2 = abs(e - k);
    for (int i = k; i <= e; i++) ans += v[i];
    ans += t2;
  } else {
    cout << "pls no";
  }
  cout << ans;
  return 0;
}
