#include <bits/stdc++.h>
long long gcd(long long a, long long b) { return (a ? gcd(b % a, a) : b); }
long long power(long long a, long long n) {
  long long p = 1;
  while (n > 0) {
    if (n % 2) {
      p = p * a;
    }
    n >>= 1;
    a *= a;
  }
  return p;
}
long long power(long long a, long long n, long long mod) {
  long long p = 1;
  while (n > 0) {
    if (n % 2) {
      p = p * a;
      p %= mod;
    }
    n >>= 1;
    a *= a;
    a %= mod;
  }
  return p % mod;
}
using namespace std;
char a[100004];
int b[100004];
int main() {
  int i, j;
  int n, p;
  scanf("%d", &n);
  scanf("%d", &p);
  scanf("%s", a);
  for (i = 0; i < n / 2; i++)
    b[i] = b[n - 1 - i] =
        min(abs(a[i] - a[n - 1 - i]), 26 - abs(a[i] - a[n - 1 - i]));
  int x = 0, h = 0, l = n / 2;
  p--;
  if (p >= n / 2) p = n - 1 - p;
  for (i = 0; i < n / 2; i++)
    if (b[i]) {
      x += b[i];
      h = max(h, i);
      l = min(l, i);
    }
  if (l == n / 2) {
    puts("0");
    return 0;
  }
  if (p <= l && l <= h)
    printf("%d\n", x + h - p);
  else if (l <= h && h <= p)
    printf("%d\n", x + p - l);
  else if (l <= p && p <= h)
    printf("%d\n", x + min(p - l + h - l, h - p + h - l));
  return 0;
}
