#include <bits/stdc++.h>
using namespace std;
const double EPS = 1e-9;
const long long INF = (int)(2e9 + 0.5);
const int MAXN = 10500;
int n, p, ans, mmin, mmax;
string s;
int main() {
  cin >> n >> p >> s;
  --p;
  if (2 * p >= n) p = n - p - 1;
  mmin = INF;
  mmax = -INF;
  for (int i = 0; i < n - i - 1; ++i) {
    int f = abs(s[i] - s[n - i - 1]);
    if (s[i] != s[n - i - 1]) {
      mmin = min(mmin, i);
      mmax = max(mmax, i);
    }
    ans += min(f, 26 - f);
  }
  if (mmin < INF && mmax > -INF) {
    if (p <= mmin)
      ans += mmax - p;
    else if (p > mmin && p <= mmax)
      ans += min(p - mmin + (mmax - mmin), mmax - p + (mmax - mmin));
    else
      ans += p - mmin;
  }
  cout << ans << endl;
  return 0;
}
