include <bits/stdc++.h>

using namespace std;

string ltrim(const string &); string rtrim(const string &);

/* * Complete the 'steadyGene' function below. * * The function is expected to return an INTEGER. * The function accepts STRING gene as parameter. */

int steadyGene(string gene) {

int n =gene.length(); int req = n/4;

map<char, int >hash ;

hash['A']=0; hash['C']=0; hash['G']=0; hash['T']=0; for(auto x: gene) hash[x]++;

int ctr = 0 ;

map<char ,int >miss;

int l = 0 , r= 0;

int ans = n ;

for(auto x: hash) { ctr+=max(0 , req-x.second); miss[x.first] = max(0 , req-x.second); }

if(ctr==0) return 0 ;

map<char, int >win;

for(int i = l ; i<=r ;i++) win[gene[i]]++;

string check="ACGT"; int m =0 ;

while(r<n) { int places=0;

for(auto x: check)
{
    if(miss[x]==0)
    places+=win[x];
}


    while(places>=ctr && l<=r)
    {

        if(places>=ctr)
        ans = min(ans , r-l+1);

        win[gene[l]]--;
        l++;
         places=0;

        for(auto x: check)
        {
            if(miss[x]==0)
            places+=win[x];
        }


    }


r++;
win[gene[r]]++;

}

return ans ; }

int main() { ofstream fout(getenv("OUTPUT_PATH"));

string n_temp;
getline(cin, n_temp);

int n = stoi(ltrim(rtrim(n_temp)));

string gene;
getline(cin, gene);

int result = steadyGene(gene);

fout << result << "\n";

fout.close();

return 0;

}

string ltrim(const string &str) { string s(str);

s.erase(
    s.begin(),
    find_if(s.begin(), s.end(), not1(ptr_fun<int, int>(isspace)))
);

return s;

}

string rtrim(const string &str) { string s(str);

s.erase(
    find_if(s.rbegin(), s.rend(), not1(ptr_fun<int, int>(isspace))).base(),
    s.end()
);

return s;

}