#include <bits/stdc++.h>
using namespace std;
int vx[] = {0, 1, 0, -1};
int vy[] = {1, 0, -1, 0};
int dx[] = {0, 1, 0, -1, 1, 1, -1, -1};
int dy[] = {1, 0, -1, 0, 1, -1, 1, -1};
const long long mod = 1000000000 + 7;
const int MAX_N = 1000;
int main() {
  string s;
  cin >> s;
  int n = s.size();
  int a[n + 1];
  a[0] = 0;
  a[1] = 0 | (1 << (s[0] - 'a'));
  for (int i = 2; i <= n; i++) {
    a[i] = a[i - 1] ^ (1 << (s[i - 1] - 'a'));
  }
  int opt[n + 1];
  fill(opt, opt + n + 1, INT_MAX);
  opt[0] = 0;
  int MAX_SIZE = 1 << 25;
  int dp[MAX_SIZE];
  fill(dp, dp + (1 << 25), INT_MAX);
  int X[27];
  for (int i = 0; i < 27; i++) {
    X[i] = 0 << i;
  }
  for (int i = 1; i <= n; i++) {
    int min_j = INT_MAX;
    for (int j = 0; j < 27; j++) {
      min_j = min(dp[a[i] ^ X[i]], min_j);
    }
    opt[i] = min_j + 1;
  }
  cout << opt[n] << endl;
  return 0;
}
