#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, p;
  string str;
  scanf("%d%d", &n, &p);
  p--;
  cin >> str;
  int firstr;
  firstr = n / 2 - 1;
  int diff = 0;
  int mini = 99999, maxi = -1;
  if (p > firstr) {
    reverse(str.begin(), str.end());
    p = n - 1 - p;
  }
  for (int i = 0; i < firstr + 1; i++) {
    if (str[i] != str[n - 1 - i]) {
      diff += min((abs(str[i] - str[n - 1 - i])),
                  abs(('z' - max(str[i], str[n - 1 - i])) +
                      min(str[i], str[n - 1 - i]) - 'a' + 1));
      mini = min(mini, i);
      maxi = max(maxi, i);
    }
  }
  if (maxi > p && mini < p) {
    if (abs(p - maxi) < abs(p - mini)) {
      diff += abs(p - maxi) * 2;
      diff += abs(p - mini);
    } else {
      diff += abs(p - mini) * 2;
      diff += abs(p - maxi);
    }
  } else if (maxi > p)
    diff += abs(p - maxi);
  else if (mini < p)
    diff += abs(p - mini);
  cout << diff;
}
