#include <cmath>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;

int main() {
    string line;
    char input;
    getline(cin, line);
    istringstream ss(line);
    vector<char> arr;
    int bigOpen = 0, bigClose = 0, mediumOpen = 0, mediumClose = 0,
        smallOpen = 0, smallClose = 0;
    bool valid = true;
    while (ss >> input) {
        if (input == '{') {
            bigOpen++;
        } else if (input == '}') {
            bigClose++;
        } else if (input == '[') {
            mediumOpen++;
        } else if (input == ']') {
            mediumClose++;
        } else if (input == '(') {
            smallOpen++;
        } else if (input == ')') {
            smallClose++;
        }
        arr.push_back(input);
        if (bigOpen < bigClose || mediumOpen < mediumClose ||
            smallOpen < smallClose) {
            valid = false;
            break;
        }
    }
    if (bigOpen - bigClose != 0 || mediumOpen - mediumClose != 0 ||
        smallOpen - smallClose != 0) {
        valid = false;
    }
    for (int i = 0; i < (arr.size() - 1); i++) {
        if (arr[i] == '(') {
            if (arr[i + 1] == ']' || arr[i + 1] == '}' || arr[i + 1] == '[' ||
                arr[i + 1] == '{') {
                valid = false;
                break;
            }
        } else if(arr[i] == '['){
            if(arr[i+1] == '}' || arr[i+1] == '{') {
                valid = false;
                break;
            }
        } else if(arr[i] == '}'){
            if(arr[i+1] == ']' || arr[i+1] == ')') {
                valid = false;
                break;
            }
        } else if(arr[i] == ']'){
            if(arr[i+1] == ')') {
                valid = false;
                break;
            }
        }
    }

    if (valid) {
        cout << "valid" << endl;
    } else {
        cout << "invalid" << endl;
    }
    return 0;
}