There are some stones on Bob's table in a row, and each of them can be red, green or blue, indicated by the characters `R`, `G`, and `B`.
Help Bob find the minimum number of stones he needs to remove from the table so that the stones in each pair of adjacent stones have different colours.
Examples:
```
"RGBRGBRGGB"   => 1
"RGGRGBBRGRR"  => 3
"RRRRGGGGBBBB" => 9
```
def solution(s):
    st=[1 for i in range(1,len(s)) if s[i-1]==s[i]]
    return sum(st)
def solution(s):
    st=[1 for i in range(1,len(s)) if s[i-1]==s[i]]
    return sum(st)