#include <bits/stdc++.h>
using namespace std;
char a[100001];
int b[100001];
int low, high;
int n;
void lowestvalue(int i) {
  int d = abs(a[i] - a[n - i + 1]);
  int c =
      abs(min(a[i], a[n - i + 1]) - 'a' + 1 + 'z' - max(a[i], a[n - i + 1]));
  if (d > c)
    b[i] = c;
  else
    b[i] = d;
}
int main() {
  int p;
  cin >> n >> p;
  for (int i = 1; i <= n; i++) cin >> a[i];
  for (int i = 1; i <= n / 2; i++) {
    if (a[i] == a[n - i + 1])
      b[i] = 0;
    else
      lowestvalue(i);
  }
  int sum = 0;
  if (n % 2 != 0 && p == (n / 2) + 1) {
    sum++;
    p--;
  } else if (p > n / 2)
    p = n - p + 1;
  int i = 1;
  while (b[i] == 0) i++;
  low = i;
  i = n / 2;
  while (b[i] == 0) i--;
  high = i;
  i = p;
  if (low > high)
    sum = 0;
  else if (p < low) {
    sum--;
    while (i <= high) {
      sum++;
      sum += b[i];
      b[i] = 0;
      i++;
    }
  } else if (p >= low && p <= high) {
    if (high - p < p - low) {
      sum--;
      while (i <= high) {
        sum++;
        sum += b[i];
        b[i] = 0;
        i++;
      }
      i--;
      sum--;
      while (i >= low) {
        sum++;
        sum += b[i];
        b[i] = 0;
        i--;
      }
    } else {
      sum--;
      while (i >= low) {
        sum++;
        sum += b[i];
        b[i] = 0;
        i--;
      }
      i++;
      sum--;
      while (i <= high) {
        sum++;
        sum += b[i];
        b[i] = 0;
        i++;
      }
    }
  } else {
    sum--;
    while (i >= low) {
      sum++;
      sum += b[i];
      b[i] = 0;
      i--;
    }
  }
  cout << sum;
  return 0;
}
