#if defined(LOCAL)
#define PROBLEM_NAME "d"
const double _max_double_error = 1e-9;
#include "testutils.h"
#define L(x...) (debug(x, #x))
#define C(x...) CHECK(x)
#else
#define L(x, ...) (x)
#define C(x, ...) ;
#include <bits/stdc++.h>
#endif

using namespace std;
using vi = vector<int>; using vvi = vector<vi>;
using ii = pair<int,int>; using vii = vector<ii>;
using l = long long; using vl = vector<l>; using vvl = vector<vl>;
using ll = pair<l,l>; using vll = vector<ll>; using vvll = vector<vll>;
using lu = unsigned long long;
using vb = vector<bool>; using vvb = vector<vb>;
using vd = vector<double>; using vvd = vector<vd>;
using mll = unordered_map<l, l>;
const l INF = numeric_limits<l>::max();
const double EPS = 1e-10; static constexpr auto PI = acos(-1);
const l e0=1, e3=1000, e5=100000, e6=10*e5, e7=10*e6, e8=10*e7, e9=10*e8;
const char lf = '\n';
#define all(x) begin(x), end(x)
#define F(a,b,c) for (l a = l(b); a < l(c); a++)
#define B(a,b,c) for (l a = l(c) - 1; a >= l(b); a--)
#define MAX(a,b)({__typeof__(a)__x=(a);__typeof__(b)__y=(b);__x<__y?__y:__x;})
#define MIN(a,b)({__typeof__(a)__x=(a);__typeof__(b)__y=(b);__x<__y?__x:__y;})

l popcnt(l value) { return __builtin_popcount(value); }
bool bit_set(l mask, l i) { return mask & (e0 << i); }

void solve(istream& cin, ostream& cout) {
  string s; cin >> s;
  l m = 0;
  vl v(1 << 26);
  for (auto c : s) {
    l t = c - 'a';
    m = m ^ (1 << t);
    if (popcnt(m) < 2) { v[m] = 1; continue; }
    v[m] = INF;
    F(i, 0, 26) if (v[m ^ (1 << i)]) v[m] = min(v[m], v[m ^ (1 << i)] + 1);
  }
  cout << v[m] << lf;
}

int main() {
  ios_base::sync_with_stdio(false); cin.tie(0);
  cout << fixed << setprecision(15);
#if defined(LOCAL)
  // _generate_random_test = generate_random;
  // _solve_brute = solve_brute;
  // _player_b = player_b;
  // _custom_solution_checker = solution_checker;
  maybe_run_tests(cin, cout);
#else
  solve(cin, cout);
#endif
}
