#include <bits/stdc++.h>
using namespace std;
const int inf = 1000000007;
const long long linf = 1ll * inf * inf;
const int N = 200000 + 7;
const int M = 31;
const int multipleTest = 0;
string s;
int n;
int dp[N];
int sub[1 << 26];
vector<int> need;
int L[N];
int calc() {
  memset(sub, 0, sizeof(sub));
  for (int i = (1), _b = (n + 1); i < _b; ++i) {
    int c = s[i - 1] - 'a';
    dp[i] = dp[i - 1] ^ (1 << c);
    sub[dp[i]] = i;
  }
  if (!dp[n]) return 0;
  memset(L, inf, sizeof(L));
  L[0] = 0;
  for (int i = (1), _b = (n + 1); i < _b; ++i) {
    for (int j = (0), _b = (26); j < _b; ++j)
      if (dp[i] & (1 << j)) {
        L[dp[i]] = min(L[dp[i]], L[dp[i] ^ (1 << j)] + 1);
      }
  }
  return L[dp[n]];
}
void solve() {
  cin >> s;
  n = (int)(s).size();
  int res = calc();
  cout << res;
}
int main() {
  int Test = 1;
  if (multipleTest) {
    cin >> Test;
  }
  for (int i = 0; i < Test; ++i) {
    solve();
  }
}
