#include <bits/stdc++.h>
% : pragma GCC optimize(2) using namespace std;
template <typename tp>
inline void read(tp &x) {
  x = 0;
  char c = getchar();
  bool f = 0;
  for (; c < '0' || c > '9'; f |= (c == '-'), c = getchar())
    ;
  for (; c >= '0' && c <= '9'; x = (x << 3) + (x << 1) + c - '0', c = getchar())
    ;
  if (f) x = -x;
}
const int N = 3e5 + 10;
int f[N], b[(1 << 27) + (1 << 4)], bit[30], n;
char str[N];
int xors = 0;
int solve(int x) {
  int ans = b[xors] + 1;
  for (int i = 0; i < 26; i++) {
    ans = min(ans, b[xors ^ bit[i]] + 1);
  }
  b[xors] = min(b[xors], ans);
  return ans;
}
int main() {
  scanf("%s", str + 1);
  n = strlen(str + 1);
  for (int i = 0; i <= 26; i++) bit[i] = (1 << i);
  memset(b, 38, sizeof(b));
  xors = 0;
  b[0] = 0;
  for (int i = 1; i <= n; i++) {
    str[i] -= 'a';
    xors ^= bit[str[i]];
    f[i] = solve(i);
  }
  cout << f[n] << "\n";
}
