#include <bits/stdc++.h>
using namespace std;
vector<int> ans;
int n, p;
char s[100010];
int solve() {
  int temp = 0, sum = 0, ss;
  for (int i = 0; i < n / 2; i++) {
    temp = abs(s[i] - s[n - i - 1]);
    temp = min(temp, 26 - temp);
    sum += temp;
    if (temp) ans.push_back(abs(i - p) < abs(n - i - p - 1) ? i + 1 : n - i);
  }
  sort(ans.begin(), ans.end());
  ss = ans.size();
  if (ss == 0) return sum;
  return sum + abs(ans[ss - 1] - ans[0]) +
         min(abs(ans[ss - 1] - p), abs(ans[0] - p));
}
int main() {
  scanf("%d%d%s", &n, &p, s);
  printf("%d\n", solve());
  return 0;
}
