#include<iostream>
#include<vector>
#include<string>
#include<algorithm>

using namespace std;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
vector<int> a[1<<26];
int main(){
    string s;
    cin >> s;
    int n = s.size();
    int tmp = 0;
    rep(i,n){
        int c = s[i]-'a';
        tmp ^= (1<<c);
        a[tmp].push_back(i+1);
    }
    int bits = 0;
    int id = 0;
    int res = 1;
    while(1){
        //cerr << id << endl;
        int mx = -1;
        int mxbits =0;
        int yy = a[bits].size();
            if(yy!=0&&a[bits][yy-1]>id){
                if(mx<a[bits][yy-1]){
                    mx = a[bits][yy-1];
                    mxbits = bits;
                }
            }
        rep(i,26){
            int k = bits ^ (1<<i);
            int xx = a[k].size();
            if(xx!=0&&a[k][xx-1]>id){
                if(mx<a[k][xx-1]){
                    mx = a[k][xx-1];
                    mxbits = k;
                }
            }
        }
        if(mx==n)break;
        res++;
        bits = mxbits;
        id = mx;
    }
    cout << res << endl;
    
    
    return 0;
}