The data of \(20\) students in a class of their weight in \(kg\) is given below. Find out the mode of their weight?
 
71, 5669, 6351, 56, 63, 69, 71, 56, 51, 63, 69, 71, 63, 51, 69, 63, 71, 56.
 
 
The mode of students weight \(=\) .