How can I get expiration date from a Future Index?

Hi,

How can I get de expiration date from a Future Index, like the Description window (attached image)? 

I tried use the code below, however dind't work.
datetime m_Expiration = (datetime)SymbolInfoInteger(_Symbol, SYMBOL_EXPIRATION_TIME);
the date returned is D'1970.01.01 00:00:00'