#include <bits/stdc++.h>
using namespace std;
bool sortbysec(const pair<int, int> &a, const pair<int, int> &b) {
  return (a.second < b.second);
}
int cnt(char a, char b) {
  int x = a - 'a';
  int y = b - 'a';
  return min(abs(x - y), 26 - abs(x - y));
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  int n, p;
  cin >> n >> p;
  p--;
  string s;
  cin >> s;
  if (p >= n / 2) {
    reverse(s.begin(), s.end());
    p = n - p - 1;
  }
  int l = -1, r = -1;
  int ans = 0;
  for (int i = 0; i < n / 2; i++) {
    if (s[i] != s[n - 1 - i]) {
      ans += cnt(s[i], s[n - 1 - i]);
      if (l == -1) l = i;
      r = i;
    }
  }
  if (l != -1) ans += min(abs(p - l), abs(r - p)) + abs(r - l);
  cout << ans;
}
