#include <bits/stdc++.h>
using namespace std;
const int N = 5e5 + 5;
const int MOD = 1e9 + 7;
int dp[(1 << 21) + 5];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  string s;
  cin >> s;
  int n = s.size();
  for (int i = 0; i < n; ++i) {
    int mask = 0;
    int id = i;
    while (id >= 0) {
      int bt = (1 << (s[id] - 'a'));
      if (mask & bt) break;
      mask ^= bt;
      --id;
      dp[mask] = __builtin_popcount(mask);
    }
  }
  for (int mask = 0; mask < (1 << 21); ++mask) {
    for (int j = 0; j < 21; ++j) {
      if ((mask & (1 << j)) == 0)
        dp[(mask | (1 << j))] = max(dp[mask], dp[(mask | (1 << j))]);
    }
  }
  int ans = 0;
  for (int mask = 0; mask < (1 << 21); ++mask) {
    int rmask = ((1 << 21) - 1) ^ mask;
    ans = max(ans, dp[mask] + dp[rmask]);
  }
  cout << ans;
  return 0;
}
