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

typedef struct ast_node ast_node;

typedef enum op {
	ADD = 0,
	SUB = 1,
	MUL = 2,
	DIV = 3,
} op;

typedef struct ast_node {
	op operation;
	int realLeft;
	int realRight;
	ast_node *right;
	ast_node *left;
} ast_node;

void freeAst(ast_node *head){
	if (head->left != NULL)
		freeAst(head->left);
	if (head->right != NULL)
		freeAst(head->left);
	free(head);
}

int exec(ast_node *exp){
	if (exp->left != NULL){
		exp->realLeft = exec(exp->left);
		freeAst(exp->left);
		exp->left = NULL;
	}
	if (exp->right != NULL){
		exp->realRight = exec(exp->right);
		freeAst(exp->right);
		exp->right = NULL;
	}

	if (exp->operation == ADD)
		return exp->realLeft+ exp->realRight;
	if (exp->operation == SUB)
		return exp->realLeft - exp->realRight;
	if (exp->operation == MUL)
		return exp->realLeft * exp->realRight;
	if (exp->operation == DIV)
		return exp->realLeft/ exp->realRight;
	return 0;
}