import math


def stadium_distance(x1, y1, x2, y2):
    """
    Calculates distance between (x1, y1) and (x2, y2) using L2-norm.
    Args:
        x1: X-coordinate of point 1.
        y1: X-coordinate of point 1.
        x2: Y-coordinate of point 2.
        y2: Y-coordinate of point 2.
    Returns:
        Distance between points (float).
    """
    return math.sqrt(((x1 - x2) ** 2) + ((y1 - y2) ** 2))