class Vector3 {
    /**
     * A 3D vector
     *
     * @param {number} x The X value of this vector
     * @param {number} y The Y value of this vector
     * @param {number} z The Z value of this vector
     */
    constructor(x, y, z) {
        this.x = x;
        this.y = y;
        this.z = z;
    }

    /**
     * Add another vector to this one
     *
     * @param {Vector3} operand The vector to add to this one
     * @returns {void}
     */
    add(operand) {
        this.x += operand.x;
        this.y += operand.y;
        this.z += operand.z;
    }
}

/**
 * Find the gravitational influence two moons have on each other
 *
 * @param {Vector3} moonA The first moon to consider
 * @param {Vector3} moonB The second moon to consider
 *
 * @returns {void}
 */
function calculateGravity(moonA, moonB) {
    
}