#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  cin >> s;
  const int n = s.size();
  int f[n + 1];
  map<int, int> g;
  f[0] = 0;
  g[0] = 0;
  for (int i = 1; i <= n; i++) {
    f[i] = f[i - 1] ^ (1 << (s[i - 1] - 'a'));
  }
  int dp[n + 1];
  dp[0] = 0;
  for (int i = 1; i <= n; i++) {
    int val = i;
    for (int j = 0; j < 26; j++) {
      int b = f[i] ^ (1 << j);
      if (g.find(b) != g.end()) val = min(val, 1 + dp[g[b]]);
    }
    if (g.find(f[i]) != g.end())
      val = min(val, 1 + dp[g[f[i]]]);
    else
      g[f[i]] = i;
    dp[i] = val;
  }
  cout << dp[n] << endl;
}
