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#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