#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
bool cmin(A &a, const B &b) {
  return a > b ? (a = b, true) : false;
}
template <typename A, typename B>
bool cmax(A &a, const B &b) {
  return a < b ? (a = b, true) : false;
}
const double PI = acos(-1);
const double EPS = 1e-9;
int inf = sizeof(int) == sizeof(long long) ? 2e18 : 1e9 + 10;
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  string s;
  cin >> s;
  vector<int> dp(1 << 26, inf);
  dp[0] = 0;
  int t = 0;
  for (int i = 0; i < s.size(); i++) {
    t ^= 1 << (s[i] - '0');
    int m = inf;
    for (int j = 0; j < 26; j++) cmin(m, dp[t ^ (1 << j)] + 1);
    cmin(dp[t], m);
  }
  cout << max(1, dp[t]) << endl;
}
