index.js

'use strict';

const fs = require('fs');

process.stdin.resume();
process.stdin.setEncoding('utf-8');

let inputString = '';
let currentLine = 0;

process.stdin.on('data', function(inputStdin) {
    inputString += inputStdin;
});

process.stdin.on('end', function() {
    inputString = inputString.split('\n');

    main();
});

function readLine() {
    return inputString[currentLine++];
}

/*
 * Complete the 'pageCount' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts following parameters:
 *  1. INTEGER n
 *  2. INTEGER p
 */

function pageCount(n, p) {
    // Write your code here
    
    let pagesBook = n;
    let pagesNumber = p;
    
    let result = 0;

    if(pagesNumber <= (pagesBook / 2)) {
        result = Math.floor(pagesNumber / 2);
        
    }else if(pagesBook % 2 === 0) {
        result = Math.ceil((pagesBook - pagesNumber) / 2);
        
    }else {
        result = Math.floor((pagesBook - pagesNumber) / 2);
    }
    
    return result;
}

function main() {
    const ws = fs.createWriteStream(process.env.OUTPUT_PATH);

    const n = parseInt(readLine().trim(), 10);

    const p = parseInt(readLine().trim(), 10);

    const result = pageCount(n, p);

    ws.write(result + '\n');

    ws.end();
}