// #define DEBUGGING
#include <bits/stdc++.h>
#define endl '\n'
#define ALL(V) (V).begin(), (V).end()
#define ALLR(V) (V).rbegin(), (V).rend()
template <typename T> using V = std::vector<T>;
template <typename T> using VV = V<V<T>>;
using ll = std::int64_t;
using ull = std::uint64_t;
using PLL = std::pair<ll, ll>;
using TLL = std::tuple<ll, ll, ll>;
template <typename T> const T& var_min(const T &t) { return t; }
template <typename T> const T& var_max(const T &t) { return t; }
template <typename T, typename... Tail> const T& var_min(const T &t, const Tail&... tail) { return std::min(t, var_min(tail...)); }
template <typename T, typename... Tail> const T& var_max(const T &t, const Tail&... tail) { return std::max(t, var_max(tail...)); }
template <typename T, typename... Tail> void chmin(T &t, const Tail&... tail) { t = var_min(t, tail...); }
template <typename T, typename... Tail> void chmax(T &t, const Tail&... tail) { t = var_max(t, tail...); }
template <typename T> const T& clamp(const T &t, const T &low, const T &high) { return std::max(low, std::min(high, t)); }
template <typename T> void chclamp(T &t, const T &low, const T &high) { return t = clamp(t, low, high); }
namespace init__ { struct InitIO { InitIO() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << std::fixed << std::setprecision(30); } } init_io; }
#define mv_rec make_v(init, tail...)
template <typename T> T make_v(T init) { return init; }
template <typename T, typename... Tail> auto make_v(T init, size_t s, Tail... tail) { return V<decltype(mv_rec)>(s, mv_rec); }
#undef mv_rec
using namespace std;
#ifdef DEBUGGING
#include "../../debug/debug.cpp"
#else
#define DEBUG(...) 0
#define DEBUG_SEPARATOR_LINE 0
#endif

const ll inf = 5e15;
V<ll> idx_v((1ll << 26), -inf);

int main() {
    string S;
    cin >> S;
    
    idx_v[0] = 0;
    V<ll> dp(S.size() + 1, inf), bits_lis(S.size() + 1, 0);
    dp[0] = 0;
    
    {
        ll cur = 0;
        for(ll i = 0; i < S.size(); i++) {
            ll n = S[i] - 'a';
            ll mask = 1ll << n;
            cur ^= mask;
            chmax(idx_v[cur], i + 1);
            bits_lis[i + 1] = cur;
        }
    }

    for(ll i = 0; i <= S.size(); i++) {
        if(dp[i] == inf) continue;
        ll cur = bits_lis[i];
        auto update = [&](ll bits) {
            ll nxt = idx_v[bits];
            if(nxt <= i) return;
            chmin(dp[nxt], dp[i] + 1);
        };
        update(cur);
        ll mask = 1;
        for(ll i = 0; i < 26; i++) {
            update(cur ^ mask);
            mask <<= 1;
        }
    }

    cout << dp.back() << endl;
    return 0;
}
