#include <bits/stdc++.h>
using namespace std;
long long pwr(long long base, long long exp, long long mod = (1000000007LL)) {
  long long res = 1;
  while (exp > 0) {
    if (exp % 2) {
      res = (res * base) % mod;
    }
    base = (base * base) % mod;
    exp /= 2;
  }
  return res;
}
const long long int N = 1e6 + 5, D = 18;
long long int n, p;
string s;
long long int val(char c) { return (long long int)(c - 'a'); }
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> p >> s;
  --p;
  long long int res = 0;
  long long int l = 0, r = n - 1;
  while (l < r) {
    long long int z = abs(val(s[l]) - val(s[r]));
    res += min(z, 26 - z);
    ++l, --r;
  }
  if (res == 0) return cout << 0, 0;
  if ((!(n & 1) && (p < n / 2)) || ((n & 1) && (p < n / 2))) {
    long long int left = n, right = 0;
    for (long long int i = 0; i < n / 2; i++) {
      if (s[i] != s[n - i - 1]) {
        left = min(left, i);
        right = max(right, i);
      }
    }
    if (p >= right)
      res += abs(p - left);
    else if (p <= left)
      res += abs(right - p);
    else {
      res += 2 * min(right - p, p - left) + max(right - p, p - left);
    }
  } else if ((!(n & 1) && (p >= n / 2)) || ((n & 1) && (p > n / 2))) {
    long long int left = n, right = 0;
    for (long long int i = n / 2; i < n; i++) {
      if (s[i] != s[n - i - 1]) left = min(left, i), right = max(right, i);
    }
    if (p >= right)
      res += abs(p - left);
    else if (p <= left)
      res += abs(right - p);
    else {
      res += 2 * min(right - p, p - left) + max(right - p, p - left);
    }
  } else {
    long long int left = n;
    for (long long int i = 0; i < n / 2; i++) {
      if (s[i] != s[n - i - 1]) left = min(left, i);
    }
    res += abs(p - left);
  }
  cout << res << '\n';
  return 0;
}
