import math


def get_distance(c1, c2):
    """ Returns approximate distance between two pairs of coordinates in km.

    Args:
        c1: coordinate pair 1
        c2: coordinate pair 2

    Returns:
        distance in km between c1 and c2
    """
    # approximate radius of earth in km
    R = 6373.0

    lat1 = math.radians(c1[0])
    lng1 = math.radians(c1[1])
    lat2 = math.radians(c2[0])
    lng2 = math.radians(c2[1])

    dlon = lng2 - lng1
    dlat = lat2 - lat1

    a = math.sin(dlat / 2)**2 + math.cos(lat1) * math.cos(lat2) * math.sin(dlon / 2)**2
    c = 2 * math.atan2(math.sqrt(a), math.sqrt(1 - a))

    distance = R * c
    return distance