#include <bits/stdc++.h>
using namespace std;
template <typename item>
item abs(item i) {
  if (i < 0) i = -i;
  return i;
}
char *s;
int n;
int pos;
int main() {
  cin >> n;
  cin >> pos;
  s = new char[n + 2];
  cin >> s + 1;
  int cnt = 0;
  if (n == 1) {
    cout << 0;
    return 0;
  }
  if (n % 2 == 1 and pos == n / 2 + 1) pos++, cnt++;
  if (pos > n / 2) pos = n - pos + 1;
  int last = n / 2, fst = 1;
  while (fst < n - fst + 1 and s[fst] == s[n - fst + 1]) fst++;
  while (last > 0 and s[last] == s[n + 1 - last]) last--;
  if (pos >= fst and pos <= last) {
    int a = pos - fst, b = last - pos;
    cnt += 2 * (min(a, b)) + max(a, b);
  } else if (pos >= fst and pos >= last)
    cnt += pos - min(fst, last);
  else if (pos <= last and pos <= fst)
    cnt += max(fst, last) - pos;
  for (int i = 1; i <= n / 2; i++) {
    int cmp = n - i + 1;
    if (s[i] > s[cmp]) swap(s[i], s[cmp]);
    int a = abs((int)(s[i] - s[cmp])), b = 'z' - s[cmp] + s[i] - 'a' + 1;
    cnt += min(a, b);
  }
  cout << cnt;
}
