#include <bits/stdc++.h>
using namespace std;
template <typename T1, typename T2>
inline void chkmin(T1 &x, T2 y) {
  if (x > y) x = y;
}
template <typename T1, typename T2>
inline void chkmax(T1 &x, T2 y) {
  if (x < y) x = y;
}
inline int readChar();
template <class T = int>
inline T readInt();
template <class T>
inline void writeInt(T x, char end = 0);
inline void writeChar(int x);
inline void writeWord(const char *s);
static const int buf_size = 4096;
inline int getChar() {
  static char buf[buf_size];
  static int len = 0, pos = 0;
  if (pos == len) {
    pos = 0, len = fread(buf, 1, buf_size, stdin);
  }
  if (pos == len) {
    return -1;
  }
  return buf[pos++];
}
inline int readChar() {
  int c = getChar();
  while (c <= 32) {
    c = getChar();
  }
  return c;
}
template <class T>
inline T readInt() {
  int s = 1, c = readChar();
  T x = 0;
  if (c == '-') s = -1, c = getChar();
  while ('0' <= c && c <= '9') x = x * 10 + c - '0', c = getChar();
  return s == 1 ? x : -x;
}
static int write_pos = 0;
static char write_buf[buf_size];
inline void writeChar(int x) {
  if (write_pos == buf_size)
    fwrite(write_buf, 1, buf_size, stdout), write_pos = 0;
  write_buf[write_pos++] = x;
}
template <class T>
inline void writeInt(T x, char end) {
  if (x < 0) writeChar('-'), x = -x;
  char s[24];
  int n = 0;
  while (x || !n) s[n++] = '0' + x % 10, x /= 10;
  while (n--) writeChar(s[n]);
  if (end) writeChar(end);
}
inline void writeWord(const char *s) {
  while (*s) writeChar(*s++);
}
struct Flusher {
  ~Flusher() {
    if (write_pos) fwrite(write_buf, 1, write_pos, stdout), write_pos = 0;
  }
} flusher;
map<vector<bool>, int> m;
vector<bool> cnt;
int main() {
  string s;
  cin >> s;
  int n = (int)(s).size();
  cnt.resize(26, 0);
  m[cnt] = 0;
  for (int i = 0; i < n; i++) {
    cnt[s[i] - 'a'] = cnt[s[i] - 'a'] ^ 1;
    int res = 1e9;
    if (m.find(cnt) != m.end()) {
      chkmin(res, m[cnt] + 1);
    }
    for (int j = 0; j < 26; j++) {
      cnt[j] = cnt[j] ^ 1;
      if (m.find(cnt) != m.end()) {
        chkmin(res, m[cnt] + 1);
      }
      cnt[j] = cnt[j] ^ 1;
    }
    if (m.find(cnt) == m.end()) {
      m[cnt] = res;
    } else {
      chkmin(m[cnt], res);
    }
    if (i == n - 1) {
      cout << res << endl;
    }
  }
  return 0;
}
