#include <bits/stdc++.h>
using namespace std;
const long long MAXN = 1e6 + 7;
const long double maxx = 1e11;
int tmp[MAXN];
int main() {
  int n, k;
  cin >> n >> k;
  string s;
  cin >> s;
  k--;
  if (k >= n / 2) k = n - k - 1;
  int ans = 0, l = 0, r = 0;
  for (int i = 0, j = n - 1; i < j; i++, j--) {
    tmp[i] = min(abs(s[i] - s[j]), 26 - abs(s[i] - s[j]));
  }
  for (int i = 1; i <= n / 2; i++) tmp[i] += tmp[i - 1];
  for (int i = 0; i < n / 2; i++) {
    if (tmp[i]) {
      l = i;
      break;
    }
  }
  for (int i = 0; i < n / 2; i++)
    if (tmp[i] == tmp[n / 2]) {
      r = i;
      break;
    }
  if (tmp[n / 2]) ans = tmp[n / 2] + min(abs(k - l), abs(k - r)) + abs(l - r);
  cout << ans << endl;
  return 0;
}
