#include <bits/stdc++.h>
using namespace std;
char s[100010];
int p, n, sum;
int main() {
  scanf("%d%d", &n, &p);
  scanf("%s", s);
  if (p > n / 2)
    p = n - p;
  else
    p--;
  int xmax = p, xmin = p;
  for (int i = 0; i < n / 2; i++) {
    if (s[i] != s[n - i - 1]) {
      xmin = min(i, xmin);
      sum += min(abs(s[i] - s[n - i - 1]), 26 - abs(s[i] - s[n - i - 1]));
      xmax = max(i, xmax);
    }
  }
  sum += (xmax - xmin) + min(abs(p - xmax), abs(p - xmin));
  printf("%d\n", sum);
  return 0;
}
