#include <bits/stdc++.h>
template <typename T1, typename T2>
std::ostream& operator<<(std::ostream& os, std::pair<T1, T2> pa) {
  return os << pa.first << " " << pa.second;
}
template <typename T>
std::ostream& operator<<(std::ostream& os, std::vector<T> vec) {
  for (int i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}
template <typename T1, typename T2>
inline bool chmax(T1& a, T2 b) {
  return a < b && (a = b, true);
}
template <typename T1, typename T2>
inline bool chmin(T1& a, T2 b) {
  return a > b && (a = b, true);
}
long long pow_mod(long long a, long long b, long long mod = -1) {
  if ((a == 0) || (mod != -1 && a % mod == 0)) {
    return 0;
  }
  long long x = 1;
  while (b > 0) {
    if (b & 1) {
      x = (mod != -1) ? (x * a) % mod : x * a;
    }
    a = (mod != -1) ? (a * a) % mod : a * a;
    b >>= 1;
  }
  return x;
}
const long long MOD = 1e9 + 7;
using ll = long long;
using P = std::pair<ll, ll>;
int main() {
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  std::string s;
  std::cin >> s;
  ll n = s.size();
  std::vector<ll> a(n + 1, 0);
  for (long long(i) = (1); i < (n + 1); i++) {
    if ((a[i - 1] >> (s[i - 1] - 'a')) & 1)
      a[i] = a[i - 1] - (1ll << (s[i - 1] - 'a'));
    else
      a[i] = a[i - 1] + (1ll << (s[i - 1] - 'a'));
  }
  std::vector<ll> dp(n + 1, 0);
  std::vector<ll> min(1ll << 26, MOD);
  min[0] = 0;
  for (long long(i) = (1); i < (n + 1); i++) {
    ll temp = min[a[i]];
    for (long long(j) = (0); j < (26); j++) chmin(temp, min[a[i] ^ (1ll << j)]);
    dp[i] = temp + 1;
    chmin(min[a[i]], dp[i]);
  }
  std::cout << dp[n] << "\n";
  return 0;
}
