#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, p, i, mn, mx, fir = -1, sec = -1, sum = 0;
  cin >> n >> p;
  string ss;
  cin >> ss;
  int PP[n];
  for (int i = 0; i < n / 2; i++) {
    mn = min(ss[i], ss[n - i - 1]) % 97;
    mx = max(ss[i], ss[n - i - 1]) % 97;
    if (mn != mx) {
      sum += min(mx - mn, 26 - mx + mn);
      if (fir == -1) fir = i + 1;
      sec = i + 1;
    }
  }
  if (n == 1)
    cout << 0;
  else if (n == 2) {
    if (fir != -1)
      cout << sum;
    else
      cout << 0;
  } else {
    if (fir == -1)
      cout << 0;
    else {
      if (n / 2 + n % 2 < p) {
        fir = n - fir + 1;
        sec = n - sec + 1;
      }
      cout << sum + min(abs(p - fir), abs(p - sec)) + abs(fir - sec);
    }
  }
}
