#include <bits/stdc++.h>
using namespace std;
const long long Mod = 1000000007;
const long long mod = 0;
struct H {
  long long x, y;
  bool operator<(const H &b) const {
    if (x != b.x) return x < b.x;
    return y < b.y;
  }
  bool operator>(const H &b) const {
    if (x != b.x) return x > b.x;
    return y > b.y;
  }
  bool operator==(const H &b) const { return x == b.x && y == b.y; }
  bool operator!=(const H &b) const { return (*this) != b; }
};
struct P {
  long long pos, cost;
  bool operator<(const P &b) const { return cost < b.cost; }
  bool operator>(const P &b) const { return cost > b.cost; }
};
struct B {
  long long to, cost;
};
struct E {
  long long from, to, cost;
  bool operator<(const E &b) const { return cost < b.cost; }
  bool operator>(const E &b) const { return cost > b.cost; }
};
template <typename T, typename U>
void chmin(T &a, U b) {
  if (a > b) a = b;
}
template <typename T, typename U>
void chmax(T &a, U b) {
  if (a < b) a = b;
}
template <typename T>
T max_0(T a) {
  if (a < 0) return 0;
  return a;
}
template <typename T>
T min_0(T a) {
  if (a > 0) return 0;
  return a;
}
long long read() {
  long long u;
  scanf("%lld", &u);
  return u;
}
long long gcd(long long i, long long j) {
  if (i > j) swap(i, j);
  if (i == 0) return j;
  return gcd(j % i, i);
}
long long mod_pow(long long x, long long n, long long p) {
  long long res = 1;
  while (n > 0) {
    if (n & 1) res = res * x % p;
    x = x * x % p;
    n >>= 1;
  }
  return res;
}
const long long Inf = 3023372036854775807;
const int inf = 1500000000;
string s;
unsigned long long dp[300000];
unsigned long long bit[1ll << 26];
signed main() {
  cin >> s;
  for (unsigned long long i = 1; i < 1ll << 26; i++) {
    bit[i] = Inf;
  }
  unsigned long long res = 0;
  for (unsigned long long i = 0; i < s.size(); i++) {
    unsigned long long t = (unsigned long long)(s[i] - 'a');
    res ^= 1ll << t;
    unsigned long long sum = bit[res];
    for (unsigned long long j = 0; j < 26; j++) {
      sum = min(sum, bit[res ^ (1ull << j)]);
    }
    bit[res] = min(bit[res], sum + 1);
    dp[i] = sum + 1;
  }
  cout << dp[s.size() - 1] << endl;
}
