#include <bits/stdc++.h>
using namespace std;
bool vis[2000005];
int dp[2000005], tog = (1 << 20) - 1;
string second;
int solve(int msk) {
  if (dp[msk] != -1) return dp[msk];
  if (vis[msk]) return dp[msk] = __builtin_popcount(msk);
  int ans = 0;
  for (int j = 0; j < 20; j++) {
    if ((1 << j) & msk) {
      ans = max(ans, solve(msk ^ (1 << j)));
    }
  }
  return dp[msk] = ans;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  memset(dp, -1, sizeof(dp));
  cin >> second;
  int ans = 0;
  vis[0] = 1;
  for (int i = 0; i < second.size(); i++) {
    int msk = 0, bt;
    for (int j = i; j < i + 20 && j < second.size(); j++) {
      bt = second[j] - 'a';
      if ((1 << bt) & msk) break;
      msk |= (1 << bt);
      vis[msk] = 1;
    }
    ans = max(ans, __builtin_popcount(msk));
  }
  for (int i = 0; i <= tog; i++) {
    int tmp = i ^ tog, on = __builtin_popcount(i), mx = solve(tmp);
    if (!vis[i]) continue;
    ans = max(ans, on + mx);
  }
  cout << ans << "\n";
  return 0;
}
