#include <bits/stdc++.h>
using namespace std;
long long arr[100005];
long long ans = 0;
long long temp[100005];
bool is(int m, string s) {
  set<char> ss;
  map<char, int> mp;
  for (int i = 0; i < m; i++) {
    ss.insert(s[i]);
    mp[s[i]]++;
  }
  if (ss.size() == ans) return true;
  for (int i = 0; i <= s.length() - m - 1; i++) {
    mp[s[i]]--;
    if (mp[s[i]] == 0) ss.erase(s[i]);
    ss.insert(s[i + m]);
    mp[s[i + m]]++;
    if (ss.size() == ans) {
      return true;
    }
  }
  return false;
}
int main() {
  int n;
  string s;
  cin >> n >> s;
  set<char> se;
  for (char c : s) se.insert(c);
  ans = se.size();
  int l = 0;
  int r = n + 1;
  while (r - l > 1) {
    int m = l + (r - l) / 2;
    if (!is(m, s))
      l = m;
    else
      r = m;
  }
  cout << r << endl;
  return 0;
}
