#include <algorithm>
#include <iostream>
using namespace std;
int main() {
string s;
cin >> s;
int cnt = 0;
int s1, s2;
for (int i = 0; i < s.size() / 2; i++) {
if (s[i] != s[s.size() - 1 - i]) {
if (s[i] > s[s.size() - 1 - i]) {
s1 = 26 - (s[i] - s[s.size() - 1 - i]);
s2 = s[i] - s[s.size() - 1 - i];
cnt += min(s1, s2);
}
else {
s1 = 26 - (s[s.size() - 1 - i] - s[i]);
s2 = s[s.size() - 1 - i] - s[i];
cnt += min(s1, s2);
}
// a b: 1 和 25
// b a: 25 和 1
}
}
cout << cnt;
}

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