#include <bits/stdc++.h>
using namespace std;
int dp[1 << 26];
int main() {
  string s;
  cin >> s;
  memset(dp, 0x3f, sizeof(dp));
  dp[0] = 0;
  int h = 0;
  for (int i = 0; i < (s.size()); i++) {
    h ^= 1 << (s[i] - 'a');
    int Min = dp[h] + 1;
    for (int j = 0; j < (26); j++) {
      if (!(h >> j & 1)) continue;
      dp[h] = min(dp[h], dp[h ^ (1 << j)] + 1);
      Min = min(Min, dp[h ^ (1 << j)] + 1);
    }
    if (i == s.size() - 1) {
      printf("%d\n", Min);
    }
  }
}
