include

using namespace std;

int test(int n, string s) { int required_count = n / 4; map mp; for (char it : s) { mp[it]++; } bool ok = true; for (auto tam : mp) { if (tam.second > required_count) { ok = false; break; } } if (ok) return 0; int min_val = n; int start = 0; for (int end = 0; end < n; end++) { mp[s[end]]--; while (mp['A'] <= required_count && mp['C'] <= required_count && mp['G'] <= required_count && mp['T'] <= required_count) { min_val = min(min_val, end - start + 1); mp[s[start]]++; start++; } } return min_val; }

int main() { int n; cin >> n; string s; cin >> s; cout << test(n, s) << endl; return 0; }