Creating a string concatenating elements of column separated by specific values

Hello

I'm trying to create VBA code to do this: I have three columns, one is the identifier of the person the other the date of the task and the other the task.
For each person I need to create a string as shown in bold in the example. The string always starts with -3 and ends with -2
All the tasks that are performed by a person the same day are separated by -1 values. Therefore every string ends always with -1-2
I should attach the excel but I'm not able to attach excel files

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It doesn't matter if in the result there are blank rows inbetween each different person as in the example. The identifiers are in column A, the date in column B, the Task (is a number) and is in column C, column D is just to show the tasks in one day but I dont have to create it, it is just to show the example, I must create the column E which is in Bold.
I need to traverse the A column keeping track of the changes in B column and adding to the string and when it changes the id I need to create a new string but I'm new to VBA and doing a mess with this

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Thanks so much mehmitcik, I think that trying to solve it with formulas is better than VBA code because I have a lot of rows to process and I might get memory error with VBA
But when executed your macro I only got one line for example, when running the macro for all this lines I only get one day activity..

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Thanks a lot!!!!!!!!!!!!!!!!!!! Great!!!!!!!!!!!!!!!!!