## https://yukicoder.me/problems/no/1924

def solve(array):
    color_set = set(array)
    if len(color_set) == 1:
        return 1
    
    mins = float("inf")
    for p in color_set:
        prev = p
        cnt = 0
        for s in array:
            if s != p:
                if prev == p:
                    cnt += 1
            prev = s
        min_a = 1 + cnt
        mins = min(mins, min_a)
    return mins




def main():
    N = int(input())
    S = input()

    answer = float("inf")
    for p1 in ["R", "G", "B"]:

        arrays = []
        prev = p1
        for s in S:
            if s != p1:
                if prev == p1:
                    arrays.append([s])
                else:
                    arrays[-1].append(s)
            prev = s

        ans = 1
        for array in arrays:
            ans += solve(array)
        answer = min(answer, ans)

    print(answer)





if __name__ == '__main__':
    main()