#include <bits/stdc++.h>
using namespace std;
const int MaxN = 200003;
int n;
char str[MaxN];
int f[MaxN], mn[1 << 27], dp[MaxN];
int main() {
  scanf("%s", str + 1);
  n = strlen(str + 1);
  for (int i = 1; i <= n; ++i) {
    f[i] = f[i - 1] ^ (1 << (str[i] - 'a'));
  }
  memset(mn, 0x7f, sizeof mn);
  mn[0] = 0;
  for (int i = 1; i <= n; ++i) {
    dp[i] = 0x7f7f7f7f;
    dp[i] = min(dp[i], mn[f[i]] + 1);
    for (int j = 0; j < 26; ++j) {
      int t = f[i] ^ (1 << j);
      dp[i] = min(dp[i], mn[t] + 1);
    }
    mn[f[i]] = min(mn[f[i]], dp[i]);
  }
  printf("%d\n", dp[n]);
  return 0;
}
