#include <bits/stdc++.h>
using namespace std;
char s[100001];
int main(void) {
  int n, p, v = 0;
  scanf("%d %d %s", &n, &p, s);
  p = min(p - 1, n - p);
  int p1 = n / 2 - 1, p2 = 0;
  for (int i = 0; i < n / 2; i++)
    if (s[i] != s[n - i - 1]) {
      int d = abs(s[i] - s[n - i - 1]);
      v += min(d, 26 - d);
      p1 = min(p1, i);
      p2 = max(p2, i);
    }
  if (v > 0) v += min(abs(p - p1), abs(p - p2)) + p2 - p1;
  printf("%d", v);
}
