#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, p;
  cin >> n >> p;
  string s, t;
  cin >> s;
  t = s;
  p--;
  int ans1 = 0, ans2 = 0, step = 0, x, last = p;
  for (int i = p;; i--, step++) {
    x = n - i - 1;
    if (s[i] != s[x])
      ans1 += step + min((s[i] - s[x] + 26) % 26, (s[x] - s[i] + 26) % 26),
          step = 0, s[i] = s[x], last = i;
    if (i == 0 || i == (n + 1) / 2) break;
  }
  step = 0;
  for (int i = last;; i++, step++) {
    x = n - i - 1;
    if (s[i] != s[x])
      ans1 += step + min((s[i] - s[x] + 26) % 26, (s[x] - s[i] + 26) % 26),
          step = 0, s[i] = s[x], last = i;
    if (i == n - 1 || i + 1 == n / 2) break;
  }
  s = t;
  step = 0, last = p;
  for (int i = p;; i++, step++) {
    x = n - i - 1;
    if (s[i] != s[x])
      ans2 += step + min((s[i] - s[x] + 26) % 26, (s[x] - s[i] + 26) % 26),
          step = 0, s[i] = s[x], last = i;
    if (i == n - 1 || i + 1 == n / 2) break;
  }
  step = 0;
  for (int i = last;; i--, step++) {
    x = n - i - 1;
    if (s[i] != s[x])
      ans2 += step + min((s[i] - s[x] + 26) % 26, (s[x] - s[i] + 26) % 26),
          step = 0, s[i] = s[x], last = i;
    if (i == 0 || i == (n + 1) / 2) break;
  }
  cout << min(ans1, ans2);
  return 0;
}
