#include <bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:1024000000,1024000000")
inline char nc() {
  static char buf[1000000], *p1 = buf, *p2 = buf;
  return p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 1000000, stdin), p1 == p2)
             ? EOF
             : *p1++;
}
inline int Scan() {
  char ch = nc();
  int sum = 0, f = 1;
  if (ch == '-') f = -1, ch = nc();
  while (!(ch >= '0' && ch <= '9')) ch = nc();
  while (ch >= '0' && ch <= '9') sum = sum * 10 + ch - 48, ch = nc();
  return sum * f;
}
int ps4[4][2] = {0, 1, 0, -1, 1, 0, -1, 0};
int ps8[8][2] = {0, 1, 0, -1, 1, 0, -1, 0, 1, 1, 1, -1, -1, -1, -1, 1};
inline int min(int a, int b, int c) { return min(a, min(b, c)); }
inline int max(int a, int b, int c) { return max(a, max(b, c)); }
inline int min(int a, int b, int c, int d) { return min(min(a, b, c), d); }
inline int max(int a, int b, int c, int d) { return max(max(a, b, c), d); }
const int N = 100005;
unordered_map<int, int> dp;
string s;
int main() {
  cin >> s;
  long long sta = 0;
  dp[sta] = 0;
  for (int i = 0; i < s.length(); ++i) {
    sta ^= (1LL << (s[i] - 'a'));
    int x = 1000000000;
    for (int i = 0; i < 26; ++i) {
      if (dp.find(sta ^ (1LL << i)) != dp.end())
        x = min(x, dp[sta ^ (1LL << i)] + 1);
    }
    if (dp.find(sta) == dp.end() && x != 1000000000) dp[sta] = x;
  }
  cout << dp[sta] << endl;
  return 0;
}
