"use strict";
var fs = require("fs");
var input = fs.readFileSync("/dev/stdin", "utf8");
var _a = input.split(" ").map(function (char) { return parseInt(char, 10); }), N = _a[0], D = _a[1];
var answer = Math.ceil(N / (D * 2 + 1));
console.log(answer);
