#include <bits/stdc++.h>
using namespace std;
#define equals(a, b) (fabs((a) - (b)) < EPS)

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

const int INF = 1 << 28;
const ll LLINF = 1LL << 60;
const double EPS = 1e-9;

int dp[1 << 26];
vector < int > range[1 << 26];
int main()
{
    int bit = 0;
    string S;

    cin >> S;
    for(int i = 0; i < S.size(); i++) {
        int nbit = bit ^ (1 << (S[i] - 'a'));
        range[bit].push_back(nbit);
        bit = nbit;
    }
    fill_n(dp, 1 << 26, INF);
    dp[0] = 0;
    for(int i = 0; i < (1 << 26); i++) {
        for(int j = 0; j < range[i].size(); j++) {
            dp[range[i][j]] = min(dp[range[i][j]], dp[i] + 1);
        }
    }

    cout << dp[bit] << endl;

    return (0);
}
        