More likely you need to change the INPUT statement.
It is not clear whether your data is in fixed columns or not. If it is in fixed columns then you don't need to do anything. If the values are free flowing then you either need either type a period where the missing value should be or switch to using a delimited file. If you make a delimited file then make sure to use the DSD option so that adjacent delimiters are interpreted as denoting a missing value.
PS: Don't use MISSOVER, unless you really want SAS to ignore values at the end of lines that are too short for the informat width being used. Use TRUNCOVER instead.