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

using namespace std;

int e[1 << 26];

int main() {
    string s;
    cin >> s;
    int n = s.size();

    int conf = 0, ans = 0;
    e[0] = 1;
    for (int i = 0; i < n; i++) {
        conf ^= 1 << (s[i] - 'a');
        int x = n + 1;
        if (e[conf])
            x = e[conf];
        for (int j = 0; j < 26; j++)
            if (e[conf ^ (1 << j)] && e[conf ^ (1 << j)] < x)
                x = e[conf ^ (1 << j)];
        if (!e[conf] || x + 1 < e[conf])
            e[conf] = x + 1;
        ans = x;
    }

    cout << ans;

    return 0;
}
