#include <stdio.h>
#include <string.h>
int main() {
char s[1001];
int a = 0;
scanf("%s", s);
int len = strlen(s);
for (int i = 0; i < len / 2; i++) {
int count = 0;
while (s[i] != s[len-1-i]) {
if((s[i] < s[len-1-i] && s[len-1-i] - s[i] <= 13) || (s[i] > s[len-1-i] && s[i] - s[len-1-i] > 13)){
if (s[i] != 'z') {
s[i] = s[i] + 1;
}else if (s[i] == 'z') {
s[i] = 'a';
}
count++;
}else if ((s[i] > s[len-1-i] && s[i] - s[len-1-i] <= 13) || (s[i] < s[len-1-i] && s[len-1-i] - s[i] > 13)) {
if (s[len-1-i] != 'z') {
s[len-1-i] = s[len-1-i] + 1;
}else if (s[len-1-i] == 'z') {
s[len-1-i] = 'a';
}
count++;
}
}
a = a + count;
}
printf("%d", a);
return 0;
}