#include <bits/stdc++.h>
using namespace std;
long long int dfs(vector<long long int>* v, long long int n) {
  long long int i, j, k, max = 0, temp;
  if (v[n].size() == 0) return 1;
  for (i = 0; i < v[n].size(); i++) {
    temp = 1 + dfs(v, v[n][i]);
    if (temp > max) max = temp;
  }
  return max;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int n, p, i, j, k, ansr1 = 0, ansr2 = 0, maxl = -1, maxr = -1;
  string s1, s2, s;
  cin >> n >> p;
  cin >> s;
  s1 = s;
  char temp;
  if (p > (n - p + 1)) p = n - p + 1;
  maxr = maxl = p - 1;
  for (i = p - 1; i <= ((n - 1) / 2); i++) {
    if (s[i] != s[n - i - 1]) {
      if ((int)s[i] < (int)s[n - i - 1]) {
        temp = s[i];
        s[i] = s[n - i - 1];
        s[n - i - 1] = temp;
      }
      ansr1 = ansr1 + min(((int)(s[i] - s[n - i - 1])),
                          ((int)(s[n - i - 1] - 'a') + 1 + (int)('z' - s[i])));
      s[i] = s[n - i - 1];
      maxr = i;
    }
  }
  ansr1 = ansr1 + (maxr - p + 1);
  for (i = p - 1; i >= 0; i--) {
    if (s[i] != s[n - i - 1]) {
      if ((int)s[i] < (int)s[n - i - 1]) {
        temp = s[i];
        s[i] = s[n - i - 1];
        s[n - i - 1] = temp;
      }
      ansr1 = ansr1 + min(((int)(s[i]) - (int)(s[n - i - 1])),
                          ((int)(s[n - i - 1] - 'a') + 1 + (int)('z' - s[i])));
      s[i] = s[n - i - 1];
      maxl = i;
    }
  }
  if (maxl != p - 1) ansr1 = ansr1 + (p - 1 - maxl) + (maxr - p + 1);
  maxr = maxl = p - 1;
  s = s1;
  for (i = p - 1; i >= 0; i--) {
    if (s[i] != s[n - i - 1]) {
      if ((int)s[i] < (int)s[n - i - 1]) {
        temp = s[i];
        s[i] = s[n - i - 1];
        s[n - i - 1] = temp;
      }
      ansr2 = ansr2 + min(((int)(s[i]) - (int)(s[n - i - 1])),
                          ((int)(s[n - i - 1] - 'a') + 1 + (int)('z' - s[i])));
      s[i] = s[n - i - 1];
      maxl = i;
    }
  }
  ansr2 = ansr2 + (p - 1 - maxl);
  for (i = p - 1; i <= ((n - 1) / 2); i++) {
    if (s[i] != s[n - i - 1]) {
      if ((int)s[i] < (int)s[n - i - 1]) {
        temp = s[i];
        s[i] = s[n - i - 1];
        s[n - i - 1] = temp;
      }
      ansr2 = ansr2 + min(((int)(s[i]) - (int)(s[n - i - 1])),
                          ((int)(s[n - i - 1] - 'a') + 1 + (int)('z' - s[i])));
      s[i] = s[n - i - 1];
      maxr = i;
    }
  }
  if (maxr != p - 1) ansr2 = ansr2 + (maxr - p + 1) + (p - 1 - maxl);
  cout << min(ansr1, ansr2);
  return 0;
}
