n = int(input())
S = input()
ans = 0
if "BB" in S:
    ans += 1
S = S.split("B")
lS = len(S)

for i in range(len(S)):

    s = len(S[i])
    if s == 0:
        continue
    if i == 0:
        if i != lS-1:
            ans += s
        else:
            ans += s-1
            
    elif i == lS-1:
        ans += s
    else:
        if s == 1:
            ans += 1
        else:
            ans += s+1
print(ans)