#include <bits/stdc++.h>
typedef long long LL;
#define SORT(c) sort((c).begin(),(c).end())
 
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
 
using namespace std;
int main(void)
{
  string s;
  cin >> s;
  int m[256];
  REP(i,26) m['a'+i]=(1<<i);
  int tmp=0;
  map<int,int> d;
  for(auto i=s.begin();i!=s.end();++i){
    tmp=(tmp^m[*i]);
    d[tmp]=-33554432;
  }
  priority_queue<pair<int,int> > q; // negc, v;
  q.push(make_pair(0,0));
  d[0]=0;
  while(!q.empty()) {
    int nc,v;
    tie(c,v) = q.top();
    q.pop();
    REP(i,26){
      if(d[v^(1<<i)]<c-1){
        q.push(make_pair(v^(1<<i),c-1));
        d[v^(1<<i)]=c-1;
      }
    }
  }
  cout << max(1,-d[tmp]) << endl;
  return 0;
}