#include <bits/stdc++.h>
using namespace std;

unsigned dp[1<<26];

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    memset(dp, 2, sizeof(dp));
    dp[0] = 0;
    string s; cin >> s;
    int curr = 0;
    for (int i = 0; i < s.size(); i++) {
        curr ^= (1 << (s[i] - 'a'));
        for (int j = 0; j < 26; j++) {
            dp[curr] = min(dp[curr], dp[curr ^ (1 << j)] + 1);
        }
    }
    if (curr == 0) dp[curr]++;
    cout << dp[curr] << "\n";
    return 0;
}