def decode$($message$\_$file$)$:

# Step $1$: Read the File

with open$($message$\_$file, $\text{'}$r$\text{'})$ as file:

content $=$ file.readlines$()$

# Step $2$: Decode the Message

decoded$\_$message $=""$

# Step $3$: Identify Triangular Numbers

triangular$\_$numbers $=$ set$()$

limit $=300$

triangular$\_$value $=0$

for num in range$(1,$ limit$+1)$:

triangular$\_$value $+=$ num

triangular$\_$numbers.add$($triangular$\_$value$)$

# Step $4$: Process Each Line

for line in content:

parts $=$ line.strip$().$split$()$

num $=$ int$($parts$[0])$

word $=$ parts$[1]$

# Step $5$: Build the Decoded Message

if num in triangular$\_$numbers:

decoded$\_$message $+=$ word $+""$

# Step $6$: Return the Result

return decoded$\_$message.strip$()$

# Example usage

message$\_$file $=$ "message.txt$"$

decoded$\_$result $=$ decode$($message$\_$file$)$

print$($decoded$\_$result$)$