#include <bits/stdc++.h>
using namespace std;
const int IINF = INT_MAX;
int getCost(char a, char b) {
  int ip = a - 'a', iq = b - 'a';
  int mini = min(max(ip, iq) - min(ip, iq), 26 + min(ip, iq) - max(ip, iq));
  return mini;
}
int compute(string s, int n, int p) {
  --p;
  int cnt = 0;
  int len = s.size();
  int answer = 0;
  int left = IINF, right = -IINF;
  for (int i = 0; i < len / 2; i++) {
    int p = i, q = len - 1 - i;
    if (s[p] != s[q]) {
      int mini = getCost(s[p], s[q]);
      answer += mini;
      left = min(left, i);
      right = max(right, i);
      ++cnt;
    }
  }
  p = min(p, n - 1 - p);
  int mini = right - left + min(abs(p - left), abs(right - p));
  if (answer == 0) mini = 0;
  return answer + mini;
}
int main() {
  int n, p;
  cin >> n >> p;
  string s;
  cin >> s;
  int answer = compute(s, n, p);
  cout << answer << endl;
  return 0;
}
