import java.io.*;

import java.lang.*;
/**
 *
 * @author Fatima
 */
class array {

    DataInputStream get  = new DataInputStream(System.in);
    int n , i, top = 0, f = 0;
    char a[];
    String str;

    void getData() {
        try {
            a = new char[30];
            System.out.println("Enter the string");
            str = get.readLine();
            n = str.length();
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }

    void push(char c) {
        a[top] = c;
        top++;
    }

    char pop() {
        char h;
        if (top != 0) {
            top--;
            h = a[top];
            return h;
        } else {
            return 0;
        }
    }

    int isEmpty() {
        if (top == 0) {
            return 1;
        } else {
            return 0;
        }
    }

    void ops() {
        char d, t;
        for (i = 0; i < n; i++) {
            d = str.charAt(i);
            switch (d) {
                case '(': {
                    push(d);
                    break;
                }
                case '{': {
                    push(d);
                    break;
                }
                case '[': {
                    push(d);
                    break;
                }
                case ')': {
                    t = pop();
                    if (t != '(') {
                        f = 1;
                    }
                    break;
                }
                case '}': {
                    t = pop();
                    if (t != '{') {
                        f = 1;
                    }
                    break;
                }
                case ']': {
                    t = pop();
                    if (t != '[') {
                        f = 1;
                    }
                    break;
                }
            }
        }
        if (f == 0 && top == 0) {
            System.out.println("Expression is valid");
        } else {
            System.out.println("Expression is invalid");
        }
    }
}

class validexpression {

    public static void main(String args[]) {
        array obj = new array();
        obj.getData();
        obj.ops();
    }
}