#include <bits/stdc++.h>
using namespace std;
const long long maxi = 1e17;
const int MAXM = 1e2 + 5;
const int MAXN = 5e2 + 5;
int main() {
  int n, p, i, j, k;
  cin >> n >> p;
  string s;
  cin >> s;
  string ss = s;
  int l = s.length();
  if (p > l / 2) {
    p = l - p + 1;
  }
  int t = -1, sum = 0, su = 0, pos = p - 1;
  for (i = p - 1; i >= 0; i--) {
    if (s[i] == s[l - i - 1]) {
      t++;
    } else {
      int x =
          min((s[i] - s[l - i - 1] + 26) % 26, (s[l - i - 1] - s[i] + 26) % 26);
      s[i] = s[l - i - 1];
      sum += x;
      t++;
      sum += t;
      t = 0;
      pos = i;
    }
  }
  t = 0;
  for (i = pos + 1; i < l / 2; i++) {
    if (s[i] == s[l - i - 1]) {
      t++;
    } else {
      int x =
          min((s[i] - s[l - i - 1] + 26) % 26, (s[l - i - 1] - s[i] + 26) % 26);
      s[i] = s[l - i - 1];
      sum += x;
      t++;
      sum += t;
      t = 0;
    }
  }
  pos = p - 1;
  s = ss;
  t = -1;
  for (i = p - 1; i < l / 2; i++) {
    if (s[i] == s[l - i - 1]) {
      t++;
    } else {
      int x =
          min((s[i] - s[l - i - 1] + 26) % 26, (s[l - i - 1] - s[i] + 26) % 26);
      s[i] = s[l - i - 1];
      su += x;
      t++;
      su += t;
      t = 0;
      pos = i;
    }
  }
  t = 0;
  for (i = pos - 1; i >= 0; i--) {
    if (s[i] == s[l - i - 1]) {
      t++;
    } else {
      int x =
          min((s[i] - s[l - i - 1] + 26) % 26, (s[l - i - 1] - s[i] + 26) % 26);
      s[i] = s[l - i - 1];
      su += x;
      t++;
      su += t;
      t = 0;
    }
  }
  cout << min(su, sum) << endl;
  return 0;
}
