#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second
template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> pip;
const ll INF = 1e9+100;
const ll MOD = 1000000007;
const double EPS = 1e-10;
const bool debug = 0;
//------------------------------//
 
string s;
int dp[212345];
 
int main() {
	cin >> s;
	int N = s.size();
	REP(i, N) s[i] -= 'a';
	
	map<int, int> m;
	
	fill(dp, dp + N + 1, INF);
	int x = 0;
	dp[0] = 0; m[0] = 0;
	REP(i, N) {
		x ^= 1<<s[i];
		int res = INF;
		
		if (m.find(x) != m.end()) chmin(res, m[x] + 1);
		REP(j, 26) if (m.find(x ^ 1<<j) != m.end()) chmin(res, m[x ^ 1<<j] + 1);
		
		if (m.find(x) == m.end() || m[x] > res]) m[x] = res;
		dp[i + 1] = res;
	}
	cout << dp[N] << endl;
	
	return 0;
}