#include <bits/stdc++.h>
using namespace std;
int main() {
  int mirror, n, p, res = 0, before = 0, after = 0, l, r;
  cin >> n >> p;
  string s;
  cin >> s;
  if (p > (n + 1) / 2)
    p = n - p;
  else
    p--;
  before = p;
  after = p;
  for (int i = 0; i < p; i++)
    if (s[i] != s[n - (i + 1)]) {
      before = i;
      break;
    }
  for (int i = p + 1; i < (n + 1) / 2; i++)
    if (s[i] != s[n - (i + 1)]) after = i;
  l = (p - before);
  r = after - p;
  res = min(r * 2 + l, l * 2 + r);
  for (int i = 0; i < (n + 1) / 2; i++) {
    mirror = n - (i + 1);
    if (s[i] != s[mirror])
      res += min(abs(s[i] - s[mirror]),
                 min(abs(s[i] + 26 - s[mirror]), abs(s[mirror] + 26 - s[i])));
  }
  cout << res;
}
