#include <bits/stdc++.h>
using namespace std;
string s;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long int n, p, l = -1, r = 0, i, j, ans = 0;
  cin >> n >> p;
  cin >> s;
  n--, p--;
  if (p > n / 2) p = n - p;
  for (i = 0; i <= n / 2; i++) {
    if (s[i] != s[n - i]) {
      long long int dif = abs(s[i] - s[n - i]);
      ans += min(dif, 26 - dif);
      if (l < 0)
        l = i;
      else
        r = i;
    }
  }
  ans += min(abs(p - l), abs(p - r));
  ans += max((r - l), 0LL);
  cout << (l < 0 ? 0 : ans) << "\n";
  return 0;
}
