#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, p, i, j, k, total = 0, c, low, high;
  char x, y;
  string s;
  cin >> n >> c;
  cin >> s;
  n--;
  c--;
  low = 0;
  high = (n - 1) / 2;
  for (i = 0; i < (n + 1) / 2; i++)
    if (s[i] == s[n - i])
      low++;
    else
      break;
  for (i = (n - 1) / 2; i >= 0; i--)
    if (s[i] == s[n - i])
      high--;
    else
      break;
  if (c > n / 2) c = n - c;
  total = high - low;
  if (c == n / 2 && n % 2 == 0)
    total = n / 2 - low;
  else {
    if (low > high) {
      cout << 0;
      return 0;
    } else if (low > c)
      total += low - c;
    else if (high < c)
      total += c - high;
    else {
      total += min(c - low, high - c);
    }
  }
  for (i = low; i < high + 1; i++) {
    k = min((s[i] - s[n - i] + 26) % 26, (s[n - i] - s[i] + 26) % 26);
    total += k;
  }
  cout << total;
}
