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

const int N = 200005;
const int inf = 1e9 + 7;

string s;
int n;
int f[N];
int g[26];
int t[1 << 26];

int main() {
	ios_base::sync_with_stdio(false); cin.tie(0);
	cin >> s;
	n = (int)s.size();
	s = ' ' + s;

	for (int mask = 0; mask < (1 << 26); ++mask) t[mask] = inf;

	f[0] = 0, t[0] = 0;
	for (int i = 1; i <= n; ++i) {
		f[i] = inf;
		g[s[i] - 'a'] ^= 1;
		int cur_mask = 0;
		for (int c = 0; c < 26; ++c) cur_mask |= (g[c] << c);
		f[i] = min(f[i], t[cur_mask] + 1);

		for (int c = 0; c < 26; ++c) {
			int mask = (cur_mask ^ (1 << c));
			f[i] = min(f[i], t[mask] + 1);
		}

		t[cur_mask] = min(f[i], t[cur_mask]);
	}	

	cout << f[n] << endl;
}