#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, p, x;
  long long int ans = 0;
  char c[100005];
  scanf("%d%d", &n, &p);
  scanf("%s", c);
  if (p > n / 2)
    p = n - p;
  else
    p--;
  int rl = -1, ll = 999999;
  for (int i = 0; i <= n / 2 - 1; i++) {
    x = min(abs(c[i] - c[n - 1 - i]),
            min(abs(c[i] + 26 - c[n - 1 - i]), abs(c[i] - 26 - c[n - 1 - i])));
    ans += x;
    if (x > 0) {
      if (rl < i) rl = i;
      if (ll > i) ll = i;
    }
  }
  if (ans != 0)
    ans += min((abs(rl - p) + abs(rl - ll)), (abs(p - ll) + abs(rl - ll)));
  printf("%lld\n", ans);
  return 0;
}
