#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

typedef struct node
{
    char el;
    struct node *left, *right;
} node;

node* create_node(char c)
{
    node *my = malloc(sizeof(*my));
    my->el = c;
    my->left = NULL;
    my->right = NULL;
    return my;
}

bool is_digit(char c)
{
    return (c >= '0' && c <= '9');
}

void error(int code)
{
    if (code == 0)
        printf("UNMATCHED BRACKETS\n");
    if (code == 1)
        printf("INCORRECT EXPRESSION\n");
    if (code == 2)
        printf("INCORRECT SYMBOL\n");
    exit(0);
}

char op;

node* expression(void);
node* summand(void);
node* multi(void);

node* build_tree(void)
{
    scanf("%c", &op);
    node *root = expression();
    if (op == '(' || op == ')')
        error(0);
    if (op == '*' || op == '+' || op == '-' || op == 'x' || op == 'X' || is_digit(op))
        error(2);
    if (op != '.')
        error(1);
    return root;
}

void print_tree(node *cur)
{
    if (cur == NULL)
        return;
    print_tree(cur->left);
    printf("%c", cur->el);
    print_tree(cur->right);
}

int calc_expression(node *cur, int x)
{
    if (cur == NULL)
        return 0;
    if (cur->left == NULL && cur->right == NULL)
    {
        if (cur->el == 'x' || cur->el == 'X')
            return x;
        return cur->el - '0';
    }
    int op1 = calc_expression(cur->left, x);
    int op2 = calc_expression(cur->right, x);
    if (cur->el == '+')
        return op1 + op2;
    if (cur->el == '-')
        return op1 - op2;
    return op1 * op2; //if cur->el == '*'
}

node* expression(void)
{
    node* left = summand();
    while (op == '+' || op == '-')
    {
        node *cur = create_node(op);
        scanf("%c", &op);
        node *right = summand();
        cur->left = left;
        cur->right = right;
        left = cur;
    }
    return left;
}

node* summand(void)
{
    node* left = multi();
    while (op == '*')
    {
        node *cur = create_node(op);
        scanf("%c", &op);
        node *right = multi();
        cur->left = left;
        cur->right = right;
        left = cur;
    }
    return left;
}

node* multi(void)
{
    if (is_digit(op) || op == 'x' || op == 'X')
    {
        node *cur = create_node(op);
        scanf("%c", &op);
        return cur;
    }
    if (op == '(')
    {
        scanf("%c", &op);
        node *cur = expression();
        if (op != ')')
            error(0);
        scanf("%c", &op);
        return cur;
    }
    if (op == ')')
        error(0); //unmatched brackets
    if (op == '.' || op == '+' || op == '-' || op == '*')
        error(1); //incorrect expresion
    error(2); //incorrect symbol in expression
    return NULL;
}

int main(void)
{
    printf("ENTER ARITHMETIC EXPRESSION WITH VARIABLE X\n");
    printf("EXPRESSION MUST CONSIST ONLY OF '*', '+', '-', digits, '(', ')' AND VARIABLES 'x' (or 'X'):\n");
    node *root = build_tree();
    printf("ENTER THE VALUE OF VARIABLE 'x' ('X'):\n");
    int x;
    scanf("%d", &x);
    //print_tree(root);
    int ans = calc_expression(root, x);
    printf("THE VALUE OF EXPRESSION AT POINT X IS %d", ans);
    return 0;
}