#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<string>
#include<cmath>
#include<algorithm>
#include<map>
#include<vector>
#include<iomanip>
#include<set>
#include<bitset>
#define endl '\n'
#define sz(s) (int)(s.size())
#define all(s) s.begin(),s.end()
#define allr(s) s.rbegin(),s.rend()
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rep1(i,n) for(int i=1;i<=(int)(n);i++)
typedef long long ll;
typedef double dl;
typedef unsigned long long ull;
const double pi = 3.14159;
using namespace std;
void fast() { ios::sync_with_stdio(0); cin.tie(0); cout.tie(0); }
int arr[26];
int main()
{
fast();
string s;
//cout << ('b' - 'a')+26 << endl;
int ans=0;
int c = 0;
//cout << char(c + 'a') << endl;
cin >> s;
s = 'a' + s;
rep1(i, s.size()-1) {
ans += min(abs(s[i] - s[i-1]), 26-abs(s[i] - s[i-1]));
}
cout << ans << endl;
//system("pause");
return 0;
}
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