#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cout << fixed;
  cout.precision(10);
  int n, p;
  cin >> n >> p;
  string s;
  cin >> s;
  --p;
  int arr[n];
  for (int i = 0; i < n; i++) {
    arr[i] = abs(s[i] - s[n - i - 1]);
    arr[i] = min(arr[i], 26 - arr[i]);
  }
  int sol = 0;
  if (p < n / 2) {
    int curr = 0;
    int left = p;
    int right = p;
    for (int i = 0; i < n / 2; i++) {
      if (arr[i]) {
        curr += arr[i];
        left = min(left, i);
        right = i;
      }
    }
    sol = curr + (right - left) + min(abs(p - left), abs(p - right));
  } else {
    int curr = 0;
    int left = p;
    int right = p;
    for (int i = n / 2; i < n; i++) {
      if (arr[i]) {
        curr += arr[i];
        left = min(left, i);
        right = i;
      }
    }
    sol = curr + (right - left) + min(abs(p - left), abs(p - right));
  }
  cout << sol;
  return 0;
}
