import java.io.*;

class Result {

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

public static int steadyGene(String gene) {
    int n = gene.length();
    int target = n / 4;
    int[] count = new int[128];

    for (char c : gene.toCharArray()) {
        count[c]++;
    }

    // If already steady
    if (count['A'] == target && count['C'] == target && count['G'] == target && count['T'] == target) {
        return 0;
    }

    int minLen = n;
    int left = 0;

    for (int right = 0; right < n; right++) {
        count[gene.charAt(right)]--;

        while (count['A'] <= target && count['C'] <= target && count['G'] <= target && count['T'] <= target) {
            minLen = Math.min(minLen, right - left + 1);
            count[gene.charAt(left)]++;
            left++;
        }
    }

    return minLen;
}

}

public class Solution { public static void main(String[] args) throws IOException { BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in)); BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

    int n = Integer.parseInt(bufferedReader.readLine().trim());
    String gene = bufferedReader.readLine();

    int result = Result.steadyGene(gene);

    bufferedWriter.write(String.valueOf(result));
    bufferedWriter.newLine();

    bufferedReader.close();
    bufferedWriter.close();
}

}