Excel - If confition then sum dynamic range/label

Excel Content

     A      B       C         D     
01    Label Value   Result  Expect result
02    Car       2       4       10
03    Car       2       4       10
04    Car       2       4       10
05    Car       2       4       10
06    Car       2       2       10
07    Van       1       2       5
08    Van       1       2       5
09    Van       1       2       5
10    Van       1       2       5
11    Van       1       1       5
12    Boat      3       6       15
13    Boat      3       6       15
14    Boat      3       6       15
15    Boat      3       6       15
16    Boat      3       3       15

i try to use if condition and sum but not work... e.g for C1 =if(A2=A3,sum(B2:B3),B2) e.g for C2=if(A3=A4,sum(B3:B4),B3)

1. I have been sorted the data by label
2. How can i count the total of value if next label is not equal ?