"use strict";

let fs = require("fs");
let rounds = parseInt(fs.readFileSync("./rounds.txt", "utf8"));

let x = 1.0;
let pi = 1.0;

for (let i = 2; i < rounds + 2; i++) {
  x *= -1;
  pi += x / (2 * i - 1);
}

pi *= 4;

console.log(pi);