#include <bits/stdc++.h>
using namespace std;
int n, p;
string s;
int mod(int a, int b) {
  int ret = a % b;
  if (ret < 0) ret += b;
  return ret;
}
int main() {
  cin >> n >> p;
  cin >> s;
  int ans = 0;
  p--;
  int a1, a2, b1, b2;
  a1 = a2 = 100005;
  b1 = b2 = -1;
  for (int i = 0; i < s.length() / 2; ++i) {
    if (s[i] != s[n - i - 1]) {
      ans += min(mod(s[n - i - 1] - s[i], 26), mod(s[i] - s[n - i - 1], 26));
      a1 = min(i, a1);
      a2 = min(n - i - 1, a2);
      b1 = max(i, b1);
      b2 = max(n - i - 1, b2);
    }
  }
  if (ans == 0) {
    cout << 0 << endl;
    return 0;
  }
  if (p >= b1 && p <= a2) {
    ans += min(abs(b2 - p), abs(p - a1));
  } else if (p >= a1 && p <= b1) {
    ans += min(abs(p - a1), abs(p - b1)) + (b1 - a1);
  } else if (p >= a2 && p <= b2) {
    ans += min(abs(p - a2), abs(p - b2)) + (b2 - a2);
  } else if (p < a1) {
    ans += min(b1 - p, mod(p - a2, n));
  } else if (p > b2) {
    ans += min(p - a2, mod(b1 - p, n));
  }
  cout << ans << endl;
  return 0;
}
