Pre-View#4A

int main(){
    std::string inp;
    std::cin >> inp;
    int a = 0;
    for(const auto c: inp){
        if( c < 0 ){ std::cout << "NOT OK"; exit(0);}
        a += (c == '(' ? 1 : -1);
    }
    std::cout << (a == 0? "OK": "NOT OK");
    return 0;
}