#include <bits/stdc++.h>
using namespace std;
int x, y, ans, st, en;
double si;
string s;
int main() {
  cin >> x >> y >> s;
  for (int i = 0, j = x - 1; i < x / 2; i++, j--) {
    if (s[i] != s[j]) {
      st = i + 1;
      break;
    }
  }
  for (int i = 0, j = x - 1; i < x / 2; i++, j--) {
    if (s[i] != s[j]) {
      en = i + 1;
    }
  }
  si = (double)(x + 1) / 2;
  if (y > si) {
    y = si - (y - si);
  }
  if (st <= y && y <= en && en != 0) {
    ans = min(abs(st - y), abs(y - en)) * 2 + max(abs(st - y), abs(y - en));
  } else if (en != 0) {
    ans = max(abs(st - y), abs(en - y));
  }
  for (int i = 0, j = x - 1; i < x / 2; i++, j--) {
    ans += min(abs(s[i] - s[j]),
               abs(min(s[i], s[j]) - 96) + abs(max(s[i], s[j]) - 122));
  }
  cout << ans << endl;
}
