#include <bits/stdc++.h>
int Dis[100001];
int GetlettersDis(char a, char b) {
  int ans = abs(a - b);
  if (ans > 13) {
    ans = 26 - ans;
  }
  return ans;
}
int main() {
  int N, P, i, Ans, Left, Right, start, end;
  char Str[100001];
  scanf("%d %d", &N, &P);
  scanf("%s", Str);
  if (P > N / 2) {
    start = N - N / 2;
    end = N;
  } else {
    start = 0;
    end = N / 2;
  }
  --P;
  Ans = 0;
  for (i = start; i < end; ++i) {
    Dis[i] = GetlettersDis(Str[i], Str[N - 1 - i]);
    Ans += Dis[i];
  }
  if (Ans == 0) {
    printf("%d\n", Ans);
    return 0;
  }
  for (i = start; i < end; ++i) {
    if (Dis[i] > 0) {
      Left = i;
      break;
    }
  }
  for (i = end - 1; i >= start; --i) {
    if (Dis[i] > 0) {
      Right = i;
      break;
    }
  }
  Ans += Right - Left;
  if (abs(P - Left) > abs(P - Right)) {
    Ans += abs(P - Right);
  } else {
    Ans += abs(P - Left);
  }
  printf("%d\n", Ans);
  return 0;
}
