#include <string>
#include <iostream>
#include <algorithm>
using namespace std;
const int inf = 1012345678;
int n, dp[200009], rb[200009], opt[(1 << 26) + 9]; string s;
int main() {
	cin >> s;
	n = s.size();
	for (int i = 0; i < 26; i++) rb[i] = (1 << i);
	int curbit = 0;
	for (int i = 1; i < 1 << 26; i++) opt[i] = inf;
	for (int i = 0; i < n; i++) {
		curbit ^= 1 << (s[i] - 97);
		dp[i + 1] = inf;
		for (int j = 0; j < 27; j++) {
			dp[i + 1] = min(dp[i + 1], opt[curbit ^ rb[j]] + 1);
		}
		opt[curbit] = min(opt[curbit], dp[i + 1]);
	}
	cout << dp[n] << endl;
	return 0;
}