#include <iostream>
#include <string>
#include <stack>

using namespace std;

int main() {
	string expression;
	stack<bool> l;

	cin >> expression;

	for (char c : expression) {
		if (c == '(') l.push(true);
		else if (c == ')') {
			if (l.empty()) {
				cout << "INVALID" << endl;
				return 0;
			}
			l.pop();
		}
	}

	if (l.size() != 0)
		cout << "INVALID" << endl;
	else
		cout << "OK" << endl;


	return 0;
}