#include <bits/stdc++.h>
using namespace std;
const int N = 250000;
const int M = 12;
const int INF = 0x3f3f3f3f;
const long long MOD = 1e9 + 7;
const double Pi = acos(-1);
int n, m;
char s[N];
int dp[1 << 27];
int main() {
  while (~scanf("%s", s)) {
    memset(dp, INF, sizeof dp);
    int tmp = 0;
    dp[0] = 0;
    int l = strlen(s);
    for (int i = 0; i < l; i++) {
      tmp ^= 1 << (s[i] - 'a');
      for (int j = 0; j < 26; j++)
        dp[tmp] = min(dp[tmp], dp[tmp ^ (1 << j)] + 1);
    }
    printf("%d\n", max(1, dp[tmp]));
  }
  return 0;
}
