#include <bits/stdc++.h>
using namespace std;
char s[200011];
int n;
map<int, int> dp;
int main() {
  int i, j, k;
  scanf("%s", s + 1);
  n = strlen(s + 1);
  dp[0] = 0;
  int f = 0;
  for (i = 1; i <= n; i++) {
    f ^= (1 << (s[i] - 'a'));
    int now = 0x3f3f3f3f;
    if (dp.find(f) != dp.end()) {
      now = min(now, dp[f]);
    }
    for (j = 0; j < 26; j++) {
      int tmp = (f ^ (1 << (j)));
      if (dp.find(tmp) != dp.end()) {
        now = min(now, dp[tmp]);
      }
    }
    if (now != 0x3f3f3f3f) {
      if (dp.find(f) == dp.end()) {
        dp[f] = now + 1;
      } else {
        dp[f] = min(dp[f], now + 1);
      }
    }
  }
  cout << dp[f] << endl;
  return 0;
}
