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Prefix: Similarly, the expression in which the operator appears before the operands is known as prefix expression. For example, +ab, where a and b are operands, + is an operator that appears before the operands a and b.

Example:

Input:  /+33-+47*+123 (Prefix)

Output:  3

Prefix:  /+33-+47*+123 

First reverse the prefix:  321+*74+-33+/

Prefix Evaluation:

Result: 3