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

#define MAX 200002

char buf[MAX];

string s;
int n;

int dp[1 << 26];

int main() {
	scanf("%s", buf);
	s = buf;
	memset(dp, -1, sizeof(dp));
	int cur = 0;
	dp[0] = 0;
	int las = 0;
	for (int i = 0; i < s.size(); i++) {
		int id = s[i] - 'a';
		cur ^= (1 << id);
		int nex = INT_MAX;
		if (dp[cur] != -1) {
			nex = min(nex, dp[cur]);
		}
		for (int j = 0; j < 26; j++) {
			int go = cur;
			go ^= (1 << j);
			if (dp[go] != -1) {
				nex = min(nex, dp[go]);
			}
		}
		if (nex != INT_MAX) {
			if (dp[cur] == -1 || dp[cur] > nex + 1) {
				dp[cur] = nex + 1;
			}
			las = nex + 1;
		}
	}
	cout << las << endl;
	return 0;
}