#include <bits/stdc++.h>
using namespace std;
inline long long bip(long long x, long long n, long long mod) {
  long long res = 1;
  while (n) {
    if (n & 1) {
      res = (res * x) % mod;
    }
    x = (x * x) % mod;
    n >>= 1;
  }
  return res;
}
const int ppr = 257;
const long long INF = 2e18;
const int inf = 998244353;
const int mod = 1e9 + 7;
const int N = 2e6 + 123;
const long double pi = 3.1741592653589793238462643;
const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};
string second;
int mx[N];
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  cin >> second;
  int n = second.size();
  second = '#' + second;
  int all = (1 << 20) - 1;
  for (int i = 1; i <= n; i++) {
    int mask = 0;
    for (int j = i; j >= 1; j--) {
      int a = int(second[j] - 'a');
      if (mask & (1 << a)) break;
      mask ^= (1 << a);
      mx[mask] = __builtin_popcount(mask);
    }
  }
  for (int i = 0; i <= all; i++)
    for (int j = 0; j < 20; j++)
      if (i & (1 << j)) mx[i] = max(mx[i], mx[i ^ (1 << j)]);
  int ans = 0;
  for (int i = 0; i <= all; i++) ans = max(ans, mx[i] + mx[i ^ all]);
  cout << ans;
  return 0;
}
