#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