excel formula help for calculate days from first min date depends on so

dear expert

i have set of so's no column A:A and dates in column B:B

i want calculate no of days gaps between first min date and second min for second so's

e.g
if 500123 repeats four times with different dates 1. 4/1/2013; 2.4/6/2013 ;3.4/16/2013 ;4.1-May-13

result
500123 4/1/2013 result 0 days because min date
500123 4/6/2013 result 5 days because 2nd min date minus from first min date
500123 4/16/2013 result 15 Days because 3rd min date minus from first min date
500123 1-May-13 result 30 Days last max date minus

find the attachment if you not understand

regards

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