Forsyth–Edwards Notation (FEN) is a standard notation for describing a particular board position of a chess game. The purpose of FEN is to provide all the necessary information to restart a game from a particular position.
Source: https://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation
a.out <FEN> [-s]
FEN - FEN to decode
-s - turns on symbol mode