#include <bits/stdc++.h>
template <class T>
bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T>
bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}
using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;
const double EPS = 1e-10;
const double PI = acos(-1.0);
const int inf = 1 << 30;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0) g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}
random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);
inline int c2i(char c) { return c - 'a'; }
int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  string in;
  cin >> in;
  int n = (int)in.size();
  const int M = 'z' - 'a' + 1;
  vi memo(1 << M, inf);
  memo[0] = 0;
  int stat = 0;
  for (int i = (int)(0); i < (int)(n); ++i) {
    int ci = c2i(in[i]);
    stat ^= (1 << ci);
    for (int k = (int)(0); k < (int)(M); ++k) {
      if ((stat >> k) & 1) {
        chmin(memo[stat], memo[stat & (~(1 << k))] + 1);
      }
    }
  }
  cout << memo[stat] << endl;
  return 0;
}
