#include<iostream>
#include<stdio.h>
#include<string>
#include<math.h>
#include<string.h>
using namespace std;
int h[30];
int main()
{
char s[1005];
scanf("%s",s);
int len=strlen(s);
int sum;
for(int i=0;i<len;i++)
{
h[s[i]-'a']++;
}
int bj=0; ///?????????
for(int i=0;i<26;i++)
{
if(h[i]%2)
bj++;
}
if(bj==1||bj==0)
sum=1;
else
sum=bj;
printf("%d\n",sum);
return 0;
}
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