#include<bits/stdc++.h>

using namespace std;

#define endl '\n'

typedef long long ll;
typedef pair<int, int> pii;

const int N = 1 << 26;
const int oo = 1e9;

int dp[N];
int n;
char s[N];

int main()
{
	ios::sync_with_stdio( 0 );
	cin.tie( 0 );

	fill(dp , dp + N, oo);

	cin >> s + 1;
	n = strlen(s + 1);

	dp[0] = 1;
	int mask = 0;
	for( int i = 1; i <= n; i++ ){
		int c  = s[i] - 'a';
		mask ^= (1 << c);
		int cnt = __builtin_popcount(mask);
		if(cnt <= 1){
			dp[mask] = 1;
		}
		else
		{
			for( int i = 0; i < 26; i++ ){
				int new_mask = mask ^ (1 << i);
				dp[mask] = min(dp[mask] , dp[new_mask]+1);
			}
		}
	}

	cout << dp[mask] << endl;
	return 0;
}

