#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, p;
  cin >> n >> p;
  p--;
  long long ans = 0;
  string s;
  cin >> s;
  if (p >= (s.size() / 2)) {
    p = n - p - 1;
  }
  long long first = p, last = p;
  for (long long i = p; i >= 0; i--) {
    if (s[i] != s[n - 1 - i]) {
      long long x = s[i] - s[n - 1 - i];
      if (x < 0) x = (-1) * x;
      x = min(x, 26 - x);
      ans += x;
      first = i;
    }
  }
  for (long long i = p + 1; i < s.size() / 2; i++) {
    if (s[i] != s[n - 1 - i]) {
      long long x = s[i] - s[n - 1 - i];
      if (x < 0) x = (-1) * x;
      x = min(x, 26 - x);
      ans += x;
      last = i;
    }
  }
  long long m1 = min(p - first, last - p);
  long long m2 = max(p - first, last - p);
  ans += (2 * m1 + m2);
  cout << ans << endl;
}
