from typing import Set


def jaccard(s1:Set[int],s2:Set[int]) -> float:
    """
    Jaccard similarity.

    Parameters
    ----------
    s1 : first set.
    s2 : second set.

    Returns
    -------
    similarity coefficient (0<=x<=1).
    """
    if len(s1|s2)==0:
        return 0.0
    else:
        return len(s1&s2)/len(s1|s2)