#include <bits/stdc++.h>
using namespace std;
int n, p, ans = 0;
string in;
vector<int> idx;
bool is_diff(int idx) { return in[idx] != in[n - idx - 1]; }
int distance(char a, char b) {
  return min(abs(a - b), min(a, b) + 26 - max(a, b));
}
int mirror(int i) { return n - i - 1; }
int calc_min_dist(int ma, int mi) {
  return min((ma - p) * 2 + p - mi, (p - mi) * 2 + ma - p);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  cin >> n >> p;
  cin >> in;
  p--;
  if (p > n / 2 - 1) {
    p = mirror(p);
  }
  bool back = false;
  int u = p;
  int t = p;
  for (int i = (0); i < (int)(n / 2); ++i) {
    if (is_diff(i)) {
      ans += distance(in[i], in[mirror(i)]);
      u = max(u, i);
      t = min(t, i);
    }
  }
  ans += calc_min_dist(u, t);
  cout << ans << '\n';
}
