int task3() {
    char c;
    cin >> c;
    if (c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z') {
        if (c >= 'a' && c <= 'z') {
            c = c - 'a' + 'A';
        }
        else {
            c = c - 'A' + 'a';
        }
    }
    cout << c;
    return 0;
}