#include<cstdio>
#include<algorithm>
using namespace std;
int D[1<<26];
int n, w[201000];
char p[201000];
int main(){
    int i, j, t;
    scanf("%s",p+1);
    for(i=1;p[i];i++){
        w[i] = w[i-1]^(1<<(p[i]-'a'));
    }
    n = i-1;
    D[0]=1;
    for(i=1;i<=n;i++){
        t = 1e9;
        for(j=0;j<26;j++){
            if(D[w[i]^(1<<j)]) t = min(t, D[w[i]^(1<<j)]+1);
        }
        if(D[w[i]])t = min(t, D[w[i]]+1);
        if(!D[w[i]] || D[w[i]]>t)D[w[i]]=t;
    }
    printf("%d\n",t-1);
}
