#include <iostream>
#include <stack>

using namespace std;

int main() {
    string s;
    cin >> s;
    bool is_ok = true;
    stack <char> v;


    for (char c : s){
        if ( c == '(' || c == '[' || c == '{'){
            v.push(c);
        }
        else {
            if (v.size() == 0){
                is_ok = false;
                break;
            }
            char top = v.top();
            if ( (c == ')' && top == '(') || (c == ']' && top == '[') || (c == '}' && top == '{'))
                v.pop();
            else {
                is_ok = false;
                break;
            }
        }
    }

    if (v.size() == 0) {
        if (is_ok)
            cout << "OK" << endl;
        else
            cout << "NOT OK" << endl;
    }
    else {
        cout << "NOT OK" << endl;
    }
    return 0;
}