#include <bits/stdc++.h>
using namespace std;
const int N = 100001, oo = 1 << 29;
const long long ooo = 1ll << 59;
const long long ADD = 1e9;
string str;
int cost[N + 10];
int fre[N + 10];
int n, p;
int main() {
  scanf("%d %d", &n, &p);
  cin >> str;
  for (int i = 1; i <= n / 2; ++i) {
    fre[(p > n / 2) ? (n - i + 1) : i] =
        min((((str[i - 1] - 'a') - (str[n - i] - 'a')) + 26) % 26,
            (((str[n - i] - 'a') - (str[i - 1] - 'a')) + 26) % 26);
  }
  if (p <= n / 2) {
    int cost = 0;
    int fNz = 0;
    for (int i = 1; i <= n / 2; ++i) {
      cost += fre[i];
      if (fNz == 0 && fre[i] != 0) fNz = i;
    }
    int lNz = 0;
    for (int i = n / 2; i >= 1; --i) {
      if (lNz == 0 && fre[i] != 0) {
        lNz = i;
        break;
      }
    }
    if (cost != 0)
      printf("%d\n", cost + (lNz - fNz) + min(abs(p - lNz), abs(p - fNz)));
    else
      puts("0");
  } else {
    int cost = 0;
    int fNz = 0;
    for (int i = n / 2 + 1; i <= n; ++i) {
      cost += fre[i];
      if (fNz == 0 && fre[i] != 0) fNz = i;
    }
    int lNz = 0;
    for (int i = n; i >= n / 2 + 1; --i) {
      if (lNz == 0 && fre[i] != 0) {
        lNz = i;
        break;
      }
    }
    if (cost != 0)
      printf("%d\n", cost + (lNz - fNz) + min(abs(p - lNz), abs(p - fNz)));
    else
      puts("0");
  }
  return 0;
}
