#include <bits/stdc++.h>
using namespace std;
const int N = 1000010;
const int MX = 123456;
const int mod = (int)1e9 + 7;
const int base = 1023456789;
const unsigned long long BS1 = 10000019ULL;
const int INF = (1 << 30);
template <class T>
inline void fastScan(T &x) {
  register char c = getchar();
  int neg = 0;
  x = 0;
  for (; (c < 48 || c > 57) && (c != '-'); c = getchar())
    ;
  if (c == '-') {
    neg = 1;
    c = getchar();
  }
  for (; c > 47 && c < 58; c = getchar()) {
    x = (x << 1) + (x << 3) + c - 48;
  }
  if (neg) x = -x;
}
int fx[] = {1, -1, 0, 0};
int fy[] = {0, 0, -1, 1};
char s[N];
int dp[1 << 26];
int main() {
  scanf("%s", s);
  int len = strlen(s);
  for (int i = 0; i < (1 << 26); i++) {
    dp[i] = 1e9;
  }
  int hand = 0;
  dp[0] = 0;
  for (int i = 0; i < len; i++) {
    hand = hand ^ (1 << (s[i] - 'a'));
    for (int j = 0; j < 26; j++) {
      dp[hand] = min(dp[hand], dp[hand ^ (1 << j)] + 1);
    }
    if (i + 1 == len) {
      printf("%d\n", dp[hand]);
    }
  }
  return 0;
}
