find minimum value for each range of numbers in a table

In column B I have a range of values and in column A a "1" is against the first few values and 2 against the next few, then 3 against the next few and so on. The number of values against 1, or 2 or 3 is variable with no pattern. How can I return a minimum value from each of the ranges of values against 1,2 and 3 respectively in a third column in the same row as the first 1, 2 or 3 in column A respectively?
A B C
1 1 50 = min value of '1' values
2 1 40
3 1 60
4 1 30
5 2 20 =min value of '2' values
6 2 10
7 2 30
8 3 50 =min value of '3' values
9 3 60
10 3 70
11 3 80
12 3 100
13 3 10
Thank you

Thank you.That works great