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

const int maxn = (int)(2e5) + 5;
map<int,int> now;
int f[maxn];
char s[maxn];

int main() {
	scanf("%s", s + 1);
	int n = strlen(s + 1), w = 0;
	memset(f, 0x3f, sizeof(f));
	now[0] = 0; f[0] = 0;
	for (int i = 1; i <= n; ++i) {
		w ^= (1 << (s[i] - 'a'));
		f[i] = min(f[i], f[i - 1] + 1);
		if (now.count(w)) f[i] = now[w] + 1;
		for (int j = 0; j < 26; ++j) {
			if (now.count(w ^ (1 << j))) f[i] = min(f[i], now[w ^ (1 << j)] + 1);
		}
		if (!now.count(w)) now[w] = f[i]; else now[w] = min(now[w], f[i]);
	}
	return printf("%d\n", f[n]), 0;
}