//task: given a string S, count how many times do you need to change letters so that every letter is different
//code

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int start_s=clock();
    std::string input;
    ifstream file;
    int random;
/* read input from file
    file.open("KB.inp");
    file >> random >> input;
    cout << "read file";
*/
/* direct input
    cin >> random >> input;
*/
    std::string alpha="abcdefghijklmnopqrstuvwxyz";
    int answer=0;
    int characterCount=0;
    int temp=0;
    cin >> input;
    int size=input.size();
    for (int i=0;i<26;i++)
    {
        temp=count(input.begin(), input.end(), alpha.at(i));
        characterCount += temp;
        if (temp>0){answer+=temp-1;}
        if (characterCount==size){break;}
    }
    cout << answer << '\n';
    int stop_s=clock();
    cout << "time: " << (stop_s-start_s)/double(CLOCKS_PER_SEC) << " seconds";
}

//input
[character count]
[string]