#include <bits/stdc++.h>
using namespace std;
void test_case() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  set<char> ss;
  for (int i = 0; i < n; ++i) {
    ss.insert(s[i]);
  }
  int unique = (int)ss.size();
  vector<bool> vis(26, false);
  vector<int> num_unique(n+1);
  num_unique[0] = 0;
  for (int i = 0; i < n; ++i) {
    if (!vis[s[i]]) {
      num_unique[i+1] = num_unique[i] + 1;
      vis[s[i]] = true;
    }
    else {
      num_unique[i+1] = num_unique[i];
    }
  }
  int i = 1, j = n, maxi = 0, ans = 0;
  while (i <= j) {
    int dist = num_unique[j]-num_unique[i];
    if (dist >= maxi) {
      maxi = dist;
      ans = j-i+1;
    }
    if (i+1 < n+1 && num_unique[i+1] == num_unique[i]) {
      ++i;
    }
    else if (j-1 > i && num_unique[j-1] == num_unique[j]) {
      --j;
    }
    else {
      ++i;
    }
  }
  cout << ans << '\n';
}
int main(int argc, char const *argv[]) {
  ios_base::sync_with_stdio(false), cin.tie(nullptr);
  int tc = 1;
  // cin >> tc;
  while (tc--) {
    test_case();
  }
  return 0;
}