import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################
n = ni()
s = input()
t = [s[0]]
for i in range(1,n):
    if s[i]!=t[-1]:
        t.append(s[i])
n = len(t)
u = []
z  = 0
for i in range(n):
    u.append(t[i])
    while len(u)>=3 and u[-1]==u[-3]:
        u.pop()
        u.pop()
        z += 1
m = len(u)
print(z+1+m*2//3)