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

typedef enum {
    TOKEN_INT,
    TOKEN_PLUS,
    TOKEN_MUL,
    TOKEN_DIV,
    TOKEN_LPAREN,
    TOKEN_RPAREN,
    TOKEN_EOF
} TokenType;

typedef struct {
    TokenType type;
    int value;
} Token;

const char *input;
size_t pos;
Token current_token;

void skip_whitespace() {
    while (isspace(input[pos])) pos++;
}

Token get_next_token() {
    skip_whitespace();

    char ch = input[pos];

    if (ch == '\0')
        return (Token){TOKEN_EOF, 0};

    if (isdigit(ch)) {
        int val = 0;
        while (isdigit(input[pos])) {
            val = val * 10 + (input[pos++] - '0');
        }
        return (Token){TOKEN_INT, val};
    }

    pos++;
    switch (ch) {
    case '+':
        return (Token){TOKEN_PLUS, 0};
    case '*':
        return (Token){TOKEN_MUL, 0};
    case '/':
        return (Token){TOKEN_DIV, 0};
    case '(':
        return (Token){TOKEN_LPAREN, 0};
    case ')':
        return (Token){TOKEN_RPAREN, 0};
    default:
        fprintf(stderr, "Unexpected character: %c\n", ch);
        exit(1);
    }
}

void eat(TokenType type) {
    if (current_token.type == type) {
        current_token = get_next_token();
    } else {
        fprintf(stderr, "Unexpected token\n");
        exit(1);
    }
}

int expr();

int factor() {
    Token tok = current_token;

    if (tok.type == TOKEN_INT) {
        eat(TOKEN_INT);
        return tok.value;
    } else if (tok.type == TOKEN_LPAREN) {
        eat(TOKEN_LPAREN);
        int result = expr();
        eat(TOKEN_RPAREN);
        return result;
    } else {
        fprintf(stderr, "Expected integer or '('\n");
        exit(1);
    }
}

int term() {
    int result = factor();
    while (current_token.type == TOKEN_MUL) {
        eat(TOKEN_MUL);
        result *= factor();
    }
    while (current_token.type == TOKEN_DIV) {
        eat(TOKEN_DIV);
        result /= factor();
    }
    return result;
}

int expr() {
    int result = term();
    while (current_token.type == TOKEN_PLUS) {
        eat(TOKEN_PLUS);
        result += term();
    }
    return result;
}

int main() {
    char buffer[256];
    printf("Enter expression: ");
    fgets(buffer, sizeof(buffer), stdin);

    input = buffer;
    pos = 0;
    current_token = get_next_token();

    int result = expr();
    if (current_token.type != TOKEN_EOF) {
        fprintf(stderr, "Unexpected extra input\n");
        return 1;
    }

    printf("Result = %d\n", result);
    return 0;
}