#include <bits/stdc++.h>
#pragma GCC optimize("O3")
namespace fastinput {
template <class T = int>
inline T readInt();
inline long double readDouble();
inline int readUInt();
inline int readChar();
inline void readWord(char *s);
inline bool readLine(char *s);
inline bool isEof();
inline int peekChar();
inline bool seekEof();
template <class T>
inline void writeInt(T x, int len = -1);
template <class T>
inline void writeUInt(T x, int len = -1);
inline void writeChar(int x);
inline void writeWord(const char *s);
inline void writeDouble(long int x, int len = 0);
inline void flush();
static const int buf_size = 4096;
static char buf[buf_size];
static int buf_len = 0, buf_pos = 0;
inline bool isEof() {
  if (buf_pos == buf_len) {
    buf_pos = 0, buf_len = fread(buf, 1, buf_size, stdin);
    if (buf_pos == buf_len) return 1;
  }
  return 0;
}
inline int getChar() { return isEof() ? -1 : buf[buf_pos++]; }
inline int peekChar() { return isEof() ? -1 : buf[buf_pos]; }
inline bool seekEof() {
  int c;
  while ((c = peekChar()) != -1 && c <= 32) buf_pos++;
  return c == -1;
}
inline int readChar() {
  int c = getChar();
  while (c != -1 && c <= 32) c = getChar();
  return c;
}
inline int readUInt() {
  int c = readChar(), x = 0;
  while ('0' <= c && c <= '9') x = x * 10 + c - '0', c = getChar();
  return x;
}
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;
}
inline long double readDouble() {
  int s = 1, c = readChar();
  long double x = 0;
  if (c == '-') s = -1, c = getChar();
  while ('0' <= c && c <= '9') x = x * 10 + c - '0', c = getChar();
  if (c == '.') {
    c = getChar();
    long double coef = 1;
    while ('0' <= c && c <= '9') x += (c - '0') * (coef *= 0.1), c = getChar();
  }
  return s == 1 ? x : -x;
}
inline void readWord(char *s) {
  int c = readChar();
  while (c > 32) *s++ = (char)c, c = getChar();
  *s = 0;
}
inline bool readLine(char *s) {
  int c = getChar();
  while (c != '\n' && c != -1) *s++ = (char)c, c = getChar();
  *s = 0;
  return c != -1;
}
static int write_buf_pos = 0;
static char write_buf[buf_size];
inline void writeChar(int x) {
  if (write_buf_pos == buf_size)
    fwrite(write_buf, 1, buf_size, stdout), write_buf_pos = 0;
  write_buf[write_buf_pos++] = (char)x;
}
inline void flush() {
  if (write_buf_pos)
    fwrite(write_buf, 1, write_buf_pos, stdout), write_buf_pos = 0;
}
template <class T>
inline void writeInt(T x, int output_len) {
  if (x < 0) writeChar('-'), x = -x;
  char s[24];
  int n = 0;
  while (x || !n) s[n++] = (char)('0' + (char)(x % 10)), x /= 10;
  while (n < output_len) s[n++] = '0';
  while (n--) writeChar(s[n]);
}
template <class T>
inline void writeUInt(T x, int output_len) {
  char s[24];
  int n = 0;
  while (x || !n) s[n++] = (char)('0' + (char)(x % 10)), x /= 10;
  while (n < output_len) s[n++] = '0';
  while (n--) writeChar(s[n]);
}
inline void writeWord(const char *s) {
  while (*s) writeChar(*s++);
}
inline void writeDouble(long int x, int output_len) {
  if (x < 0) writeChar('-'), x = -x;
  int t = (int)x;
  writeUInt(t), x -= t;
  writeChar('.');
  for (int i = output_len - 1; i > 0; i--) {
    x *= 10;
    t = std::min(9, (int)x);
    writeChar('0' + t), x -= t;
  }
  x *= 10;
  t = std::min(9, (int)(x + 0.5));
  writeChar('0' + t);
}
}  // namespace fastinput
using namespace fastinput;
using namespace std;
const int N = 2e5 + 10;
int masked[1 << 26];
int masks[N];
int dp[N];
int popcnt(int x) {
  int keep = 0;
  while (x) {
    x = x & (x - 1);
    ++keep;
  }
  return keep;
}
int main() {
  string s;
  cin >> s;
  int n = s.length();
  int curmask = 0;
  memset(masked, -1, sizeof(masked));
  masks[0] = 0;
  masked[0] = 0;
  for (int i = 0; i < n; ++i) {
    curmask ^= 1 << (s[i] - 'a');
    masks[i + 1] = curmask;
    masked[curmask] = i + 1;
  }
  if (masked[0] == n) {
    cout << 1 << endl;
    return 0;
  }
  for (int i = 0; i <= n; ++i) dp[i] = n + 1;
  dp[0] = 0;
  for (int i = 0; i < n; ++i) {
    int pr = masks[i];
    int go = -1;
    for (int j = 0; j < 26; ++j) {
      int shifted = pr ^ (1 << j);
      if (masked[shifted] != -1) {
        int go = masked[shifted];
        if (go > i) {
          dp[go] = min(dp[go], dp[i] + 1);
        }
      }
    }
    if (masked[pr] != i) {
      dp[masked[pr]] = min(dp[masked[pr]], dp[i]);
    }
  }
  cout << dp[n] << endl;
  return 0;
}
