#include <iostream>
#include <set>
#include <map>
using namespace std;


int main()
{
int n;
cin >> n;
string s;
cin >> s;
set<char> st;
for(int i = 0; i < s.size(); i++) {
st.insert(s[i]);
}
map<char, int> cnt;
int result = 2e9;
int unique_chars = st.size();
int curr_uni = 0;
int j = 0;
for(int i = 0; i < n; i++) {

while(j < n and curr_uni < unique_chars) {
if(cnt[s[j]] == 0) {
curr_uni++;
}
cnt[s[j]]++;
if(curr_uni == unique_chars) {
result = min(result, j - i + 1);
break;
}
j++;
}
int i_tmp = i;
while(i < n and curr_uni == unique_chars) {
result = min(result, j - i + 1);
if(cnt[s[i]] == 1) {
curr_uni--;
break;
}
cnt[s[i]]--;
i++;
}
// i--;
}

cout << result << endl;
return 0;
}

// 7
//aaBCCee