When choosing a sentinel value,you should choose a value that would never be encountered in the input of the program.

This is because the sentinel value is used to indicate the end of input or a special condition, such as an error. If the value chosen as a sentinel can be encountered in the input, it may cause the program to terminate prematurely or produce unexpected results. Therefore, it is essential to choose a sentinel value that is not commonly encountered in the input to avoid such problems.