#include <bits/stdc++.h>
using namespace std;
const int dx44[5] = {0, -1, -1, 1, 1};
const int dy44[5] = {0, -1, 1, -1, 1};
const int dx4[5] = {0, -1, 0, 1, 0};
const int dy4[5] = {0, 0, 1, 0, -1};
const int dx8[9] = {0, -1, 0, 1, 0, 1, 1, -1, -1};
const int dy8[9] = {0, 0, 1, 0, -1, 1, -1, 1, -1};
const int maxn = 2e5 + 5;
const double PI = acos(-1.0);
const long long mod = 1e9 + 7;
long long po(long long a, long long b, long long mod) {
  long long res = 1;
  a %= mod;
  for (; b; b >>= 1) {
    if (b & 1) res = res * a % mod;
    a = a * a % mod;
  }
  return res;
}
long long gcd(long long a, long long b) {
  if (a == 0) {
    return b;
  } else {
    return gcd(b % a, a);
  }
}
void YES() {
  puts("YES");
  exit(0);
}
void Yes() { puts("Yes"); }
void NO() {
  puts("NO");
  exit(0);
}
void No() { puts("No"); }
void one() {
  puts("-1");
  exit(0);
}
int dp[maxn], f[70000010];
char x[maxn];
void solve() {
  scanf("%s", x + 1);
  int len = strlen(x + 1);
  int sum = 0;
  memset(f, 0x3f, sizeof(f));
  f[0] = 0;
  for (int i = 1; i <= len; i++) {
    int y = (1 << (int)(x[i] - 'a'));
    sum ^= y;
    dp[i] = 0x3f;
    dp[i] = min(dp[i], f[sum] + 1);
    for (int j = 0; j < 26; j++) {
      dp[i] = min(dp[i], f[sum ^ (1 << j)] + 1);
    }
    f[sum] = min(f[sum], dp[i]);
  }
  printf("%d\n", dp[len]);
}
int main() {
  solve();
  return 0;
}
