#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:134217728")
const long long MOD = 1000000007;
const long long INF = 2000000001;
const double EPS = 1e-9;
const int HASH_POW = 13;
const double PI = acos(-1.0);
using namespace std;
int l = -1, r = -1;
int main() {
  cin.sync_with_stdio(0);
  int n, p;
  string s;
  cin >> n >> p >> s;
  --p;
  if (p >= n / 2) {
    p = n - 1 - p;
    reverse(s.begin(), s.end());
  }
  int ans = 0;
  for (int i = 0; i < n / 2; ++i) {
    if (s[i] != s[n - 1 - i]) {
      ans += min(abs(s[i] - s[n - 1 - i]), 26 - abs(s[i] - s[n - 1 - i]));
      if (l == -1) l = i;
      r = i;
    }
  }
  if (l != -1) {
    if (p < l) {
      ans += r - p;
    } else if (p <= r) {
      ans += r - l + min(p - l, r - p);
    } else {
      ans += p - l;
    }
  }
  printf("%d\n", ans);
  return 0;
}
