#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<char, int>;
const int inf = numeric_limits<int>::max() / 3;
int bit[100010];
int dp[100000000];
int main(void) {
  string s;
  cin >> s;
  int n = (int)s.size();
  fill(bit, bit + 100010, 0);
  fill(dp, dp + 100000000, inf);
  bit[0] = 0;
  for (int i = 0; i < n; ++i) {
    bit[i + 1] = bit[i] ^ (1 << s[i] - 'a');
  }
  dp[0] = 0;
  for (int i = 1; i <= n; ++i) {
    int calc = dp[bit[i]] + 1;
    for (int j = 0; j < 26; ++j) {
      int mask = 1 << j;
      calc = min(calc, dp[bit[i] ^ mask] + 1);
    }
    dp[bit[i]] = min(dp[bit[i]], calc);
    if (i == n) cout << calc << endl;
  }
  return 0;
}
