/*
 *  Author: Arpit Bhayani
 *  https://arpitbhayani.me
 */
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <climits>
#include <deque>
#include <iostream>
#include <list>
#include <limits>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <vector>

#define ll long long

#define MIN(a, b) a < b ? a : b
#define MAX(a, b) a > b ? a : b

using namespace std;

int readline(char *str) {
    int i = 0;
    char ch;
    while((ch = getchar()) != '\n') {
        str[i++] = ch;
    }
    str[i] = '\0';
    return i;
}

struct node {
    int val;
    struct node * left;
    struct node *right;
};


struct node * new_node(int val) {
    struct node *t = (struct node *) malloc(sizeof(struct node));
    t->val = val;
    t->left = t->right = NULL;
    return t;
}

int _is_valid_bst(struct node * root, long long int * m) {
    if(root == NULL) {
        return 1;
    }

    int l = _is_valid_bst(root->left, m);

    if(root->val <= *m) {
        return 0;
    }
    else {
        *m = root->val;
    }

    int r = _is_valid_bst(root->right, m);

    return l && r;
}

int is_valid_bst(struct node * root) {
    long long int m = (long long int) INT_MIN - 1;
    return _is_valid_bst(root, &m);
}

int main(int argc, char *argv[]) {
    struct node * root = NULL;

    root = new_node(1);
    root->left = new_node(1);
    // root->right = new_node(15);
    // root->right->left = new_node(6);
    // root->right->right = new_node(20);

    printf("%d\n", is_valid_bst(root));

    return 0;
}