def policy_compare(sen_a, sen_b, voting_dict):
    """
    Input: last names of sen_a and sen_b, and a voting dictionary mapping senator
           names to lists representing their voting records.
    Output: the dot-product (as a number) representing the degree of similarity
            between two senators' voting policies
    Example:
        >>> voting_dict = {'Fox-Epstein':[-1,-1,-1,1],'Ravella':[1,1,1,1]}
        >>> policy_compare('Fox-Epstein','Ravella', voting_dict)
        -2
    """
    return sum([voting_dict[sen_a][i]*voting_dict[sen_b][i] for i in range(len(voting_dict[sen_a]))])