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


int main()
{
    int n;
    cin >> n;
    string s;
    cin >> s;
    map<char, int> mapa;
    int j = 0;
    int result = 2e9;
    for(int i = 0; i < n; i++) {
        mapa[s[i]]++;
        int k = mapa[s[i]];
        while(mapa[s[j]] > 1) {
            mapa[s[j]]--;
            j++;
        }
        if(k == 1) {
            result = i - j + 1;
        }
        else {
            result= min(result, i - j + 1);
        }
    }
    cout << result << endl;
    return 0;
}

// 7
//aaBCCee