Challenge page : http://www.ancientsocieties.com/moshi-moshi/
There is no Challenge Text, but a screenshot of a mobile phone.
The title of the Challenge is a clue to solve it as Moshi Moshi are the Japanese words use to say Hello on the phone.
First of all, convert the letters from the week challenge into numbers thanks to a phone dialer :
Sarajevo = 72725386
Villa = 84552
Milk = 6455
Dakota = 325682
Polonium210 = 76566486210
Then, make the calculations adding or subtracting the ones from the screenshot.
Sarajevo = 72725386 – 72697413 = 27973
Villa = 84552 – 56716 = 27836
Milk = 6455 + 24827 = 31282
Dakota = 325682 – 298257 = 27425
Polonium210 = 76566486210 – 76566449140 = 37070
We finally get this sequence :
27973
27836
31282
27425
37070
Those numbers are UNICODE numbers of Japanese Kanji characters : 浅沼稲次郎 which is translated to Inejiro Asanuma.
The solution is 浅沼稲次郎 or InejiroAsanuma
The solution page is http://stl.la/inejiroasanuma, this page is redirected to http://www.ancientsocieties.com/inejiro-asanuma/