function mcpi(n) {
    var x, y, m = 0;

    for (var i = 0; i < n; i += 1) {
        x = Math.random();
        y = Math.random();

        if (x * x + y * y < 1) {
            m += 1;
        }
    }

    return 4 * m / n;
}

console.log(mcpi(1000));
console.log(mcpi(10000));
console.log(mcpi(100000));
console.log(mcpi(1000000));
console.log(mcpi(10000000));