def signed_pattern_positions(pi, pat):
    signs = [1 if e > 0 else -1 for e in pat]
    perm = [e if e > 0 else -e for e in pat]
    lpi = list(pi)
    result = []
    for occ in pi.permutation().pattern_positions(perm):
        if all((e > 0) == (lpi[i] > 0) for i, e in zip(occ, signs)):
            result.append(occ)
    return result

def statistic(pi):
    return len(signed_pattern_positions(pi, [1,-2]))