#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long n, p, pos1, pos2, ans, i;
  string s;
  cin >> n >> p;
  cin >> s;
  p--;
  ans = 0;
  pos1 = -1;
  for (i = 0; i < n / 2; i++) {
    if (s[i] != s[n - 1 - i]) {
      ans = ans + min(abs(s[i] - s[n - i - 1]),
                      (min('z' - s[i], 'z' - s[n - i - 1]) +
                       min(s[i] - 'a', s[n - 1 - i] - 'a') + 1));
      pos1 = i;
      break;
    }
  }
  pos2 = -1;
  for (i = pos1 + 1; i < n / 2; i++) {
    if (s[i] != s[n - 1 - i]) {
      ans = ans + min(abs(s[i] - s[n - i - 1]),
                      (min('z' - s[i], 'z' - s[n - i - 1]) +
                       min(s[i] - 'a', s[n - 1 - i] - 'a') + 1));
      pos2 = i;
    }
  }
  if (p >= n / 2) p = n - p - 1;
  if (pos1 == -1 && pos2 == -1)
    cout << "0" << endl;
  else if (pos2 == -1) {
    ans = ans + abs(p - pos1);
    cout << ans << endl;
  } else {
    ans = ans + (pos2 - pos1) + min(abs(pos1 - p), abs(pos2 - p));
    cout << ans << endl;
  }
  return (0);
}
