SOM.ALS to refer to other cells as criterium

[CiliaJ1010]

Hello everyone, 

I have a problem with the SOM.ALS (SUMIF function in English) function. I have a very large file of numbers, this is a small part of it. If want to know the total amount of days a customer has stayed in a hotel. But some customers have stayed for multiple days (customer 1 has stayed 2 times, 30 days in total). How do I create a formule that I can add up the days in the hotel, dependent on the customer number. 

If now use this: SOM.ALS(A2:A6900; "1"; F2:F6900), but then I have to manually chance the criterium each time. 

Customer number	Days in Hotel
1	1
1	29
2	3
3	1
3	2
4	3
5	5
5	9
6	3
6	1
6	0
8	5
9	1
10	2
10	9
10	9
10	2
10	1
10	1

[#2 · Accepted solution]

@CiliaJ1010 I would create a pivot table. See attached.