#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1000000007;
long long POW(long long a, long long b, long long MMM = MOD) {
  long long ret = 1;
  for (; b; b >>= 1, a = (a * a) % MMM)
    if (b & 1) ret = (ret * a) % MMM;
  return ret;
}
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
long long lcm(long long a, long long b) {
  if (a == 0 || b == 0) return a + b;
  return a * (b / gcd(a, b));
}
int dx[] = {0, 1, 0, -1, 1, 1, -1, -1}, dy[] = {1, 0, -1, 0, 1, -1, 1, -1};
int d[1 << 26];
char s[200001];
int main() {
  fill(d, d + (1 << 26), 987654321);
  d[0] = 1;
  int now = 0, n;
  scanf("%s", s);
  n = strlen(s);
  for (int(i) = (0); (i) <= (n - 1); (i) += (1)) {
    s[i] -= 'a';
    now ^= (1 << s[i]);
    bitset<26> bs = now;
    if (bs.count() <= 1) d[now] = 1;
    for (int(k) = (0); (k) <= (25); (k) += (1)) {
      if (now & (1 << k)) {
        int kk = now ^ (1 << k);
        if (d[kk] != 987654321) d[now] = min(d[now], d[kk] + 1);
      }
    }
  }
  printf("%d", d[now]);
}
