#include <bits/stdc++.h>
using namespace std;
inline int read() {
  int x = 0;
  char ch = getchar();
  bool positive = 1;
  for (; !isdigit(ch); ch = getchar())
    if (ch == '-') positive = 0;
  for (; isdigit(ch); ch = getchar()) x = x * 10 + ch - '0';
  return positive ? x : -x;
}
inline void write(int a) {
  if (a >= 10) write(a / 10);
  putchar('0' + a % 10);
}
inline void writeln(int a) {
  if (a < 0) {
    a = -a;
    putchar('-');
  }
  write(a);
  puts("");
}
string s;
int dp[1 << 27], sum, oo = 10000005;
int main() {
  cin >> s;
  dp[0] = 1;
  for (int i = 0; i < s.length(); i++) {
    sum ^= 1 << (s[i] - 'a');
    if (!dp[sum])
      dp[sum] = oo;
    else
      continue;
    for (int j = 0; j < 26; j++)
      if (dp[sum ^ (1 << j)]) dp[sum] = min(dp[sum], dp[sum ^ (1 << j)] + 1);
  }
  if (sum == 0)
    writeln(1);
  else
    writeln(dp[sum] - 1);
}
