#include <cstdio>
#include <algorithm>
#include <string>
#include <cstring>
#include <map>
#define N 200005
#define fi(a, b, c) for(int a = (b); a < (c); a++)
#define FI(a, b, c) for(int a = (b); a <= (c); a++)
using namespace std;

int n, dp[N], best[1 << 26];
char s[N];

int main(){
	scanf("%s", s);
	n = strlen(s);
	
	int mask = 0;
	fi(i, 0, 1 << 26) best[i] = 1e9;
	best[0] = 0;
	
	fi(i, 0, n){
		mask ^= 1 << s[i] - 'a';
		
		dp[i] = best[mask] + 1;
		fi(j, 0, 26){
			dp[i] = min(dp[i], best[mask ^ 1 << j] + 1);
		}
		
		best[mask] = min(best[mask], dp[i]);
	}
	
	printf("%d\n", dp[n - 1]);
}