import std.stdio, std.string, std.conv, std.algorithm;
import std.range, std.array, std.math, std.typecons, std.container, core.bitop;


void main() {
    string s;
    scan(s);
    int n = s.length;
    auto a = new int[](n + 1);

    foreach (i ; 0 .. n) {
        a[i + 1] = a[i] ^ (1 << (s[i] - 'a'));
    }

    debug {
        writeln(a);
    }

    auto opt = new int[](n + 1);
    auto dp = new int[](1<<26);
    dp[] = n;
    dp[0] = 0;

    foreach (i ; 1 .. n + 1) {
        int mn = dp[a[i]];

        foreach (j ; 0 .. 26) {
            mn = min(mn, dp[a[i] ^ (1<<j)]);
        }

        opt[i] = mn + 1;
        dp[a[i]] = min(dp[a[i]], opt[i]);

        debug {
            writeln(opt);
        }
    }

    writeln(opt[n]);
}



void scan(T...)(ref T args) {
    string[] line = readln.split;
    foreach (ref arg; args) {
        arg = line.front.to!(typeof(arg));
        line.popFront();
    }
    assert(line.empty);
}



void fillAll(R, T)(ref R arr, T value) {
    static if (is(typeof(arr[] = value))) {
        arr[] = value;
    }
    else {
        foreach (ref e; arr) {
            fillAll(e, value);
        }
    }
}