#include <bits/stdc++.h>
using namespace std;
int dist(char a, char b) {
  if (a > b) swap(a, b);
  return min(abs(a - b), a - 'a' + 'z' - b + 1);
}
int main() {
  int n, p;
  cin >> n >> p;
  string s;
  cin >> s;
  string s1 = s.substr(0, n / 2);
  reverse(s.begin(), s.end());
  string s2 = s.substr(0, n / 2);
  int d = min(p, n - p + 1) - 1, res1 = 0, res2 = 0, res = 0;
  for (int i = 0; i < n / 2; i++) res += dist(s1[i], s2[i]);
  for (int i = d, j = 0; i < n / 2; i++, j++)
    if (dist(s1[i], s2[i])) res1 = j;
  for (int i = d, j = 0; i >= 0; i--, j++)
    if (dist(s1[i], s2[i])) res2 = j;
  cout << res + res1 + res2 + min(res1, res2);
}
