#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 1;
char s[N];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n, p;
  cin >> n >> p;
  cin >> s;
  --p;
  if (p >= n / 2) p = n - p - 1;
  int ans = 0;
  int L = INT_MAX, R = INT_MIN;
  bool flag = false;
  for (int i = 0; i < n / 2; ++i) {
    if (s[i] != s[n - 1 - i]) {
      flag = true;
      L = min(L, i);
      R = max(R, i);
      ans += min(abs(s[n - i - 1] - s[i]),
                 26 - max(s[i], s[n - i - 1]) + min(s[i], s[n - i - 1]));
    }
  }
  if (flag) {
    if (p < L)
      ans += R - p;
    else if (p > R)
      ans += p - L;
    else
      ans += min(p - L, R - p) + R - L;
  }
  cout << ans << '\n';
  return 0;
}
