#include <bits/stdc++.h>
#include <stdio.h>
using namespace std;

#define INF 2147483647
#define LINF 9223372036854775807
#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(), (v).end()

typedef long long ll;
typedef pair<ll, int> P;

string s;
int cnt[26][200000],cnt2[26];
int ans;
bool flg;
int fst,snd;

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);

	cin>>s;
	REP(i,s.size()) {
		if(i!=0){
			REP(j,26) cnt[j][i]=cnt[j][i-1];
		}
		cnt[s[i]-'a'][i]++;
		cnt2[s[i]-'a']++;
	}


	bool ok=false;
	REP(i,26) {
		if(cnt2[i]%2==1) ok=true;
	}
	if(!ok) {
		cout<<'1'<<endl;
		return 0;
	}

	REP(i,26) flg[i]=false;

	REP(i,s.size()) {
		if(cnt2[s[i]-'a']==1) {
			ans++;
			if(!flg) flg=true,fst=i,snd=i;
			else {
				fst=snd,snd=i;
				REP(j,26) {
					if(s[i]-'a'==j) continue;
					if((cnt2[j]-cnt[j][fst])%2==1&&cnt2[j]!=1) {
						ans++;
					}
				}
			}
		}
	}
	REP(i,26) {
		if(cnt2[i]%2==1&&cnt2[i]!=1) ans++;
	}
	cout<<ans<<endl;

	return 0;
}
