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

int main() {
    string s; cin >> s;
    int bits = 0;
    vector<int> dp(1<<26, 1e9);
    dp[0] = 0;
    for (char c : s) {
        bits ^= 1 << (c-'a');
        for (int i = 0; i < 26; ++i) {
            dp[bits] = min(dp[bits], dp[bits ^ (1<<i)] + 1);
        }
    }
    cout << max(1,dp[bits]) << endl;
    return 0;
}
