#include <bits/stdc++.h>
using namespace std;
const int N = 2e6 + 100;
const int ALP = 26;
map<int, int> dp;
char str[N];
int main(int, char **) {
  scanf("%s", str);
  int len = strlen(str);
  int cur = 0;
  dp[0] = 0;
  for (int i = 0; i < len; i++) {
    cur ^= (1 << (str[i] - 'a'));
    int cdp = N;
    if (dp.count(cur)) cdp = dp[cur];
    for (int j = 0; j < ALP; j++) {
      if (dp.count(cur ^ (1 << j))) cdp = min(cdp, dp[cur ^ (1 << j)] + 1);
    }
    if (!dp.count(cur))
      dp[cur] = cdp;
    else
      dp[cur] = min(dp[cur], cdp);
    if (i == len - 1) printf("%d\n", cdp);
  }
  return 0;
}
