How to get Total reach using facebook insight Graph api

anyone can help on facebook insights? I'm trying to get the Total Reach using facebook graph API.

Here's my example:

http://ift.tt/1BT4Rbs

I've been trying these following metrics:

• /page_impressions_frequency_distribution


• /page_impressions_viral_frequency_distribution

But I still can't get the right value for the Total Reach.

Anybody can help me?

Thanks in advance.