#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
    string s;
    cin>>s;

    int N = (int)s.size();
    vector<int> T(1<<26, N);
    T[0] = 0;

    int h = 0;
    for (int i=0; i<(int)s.size(); i++)
    {
        h ^= 1<<(s[i]-'a');
        int a = N;
        for (int i=0; i<26; i++)
            a = min(a, T[h^1<<i]+1);
        T[h] = min(T[h], a);
    }
    cout<<max(T[h], 1)<<endl;
}
