#include<bits/stdc++.h>
using namespace std;
int main(){
int n;
string s;
cin>>n>>s;
deque<char> dq;
int cnt=0;
for (char c:s){

if(dq.size()>=1 and dq.end()[-1]==c){
++cnt;
continue;
}
if(dq.size()>=2 and dq.end()[-2]==c){
++cnt;
dq.pop_back();
continue;
}
dq.push_back(c);
}

int siz=dq.size();
cnt+=(siz+2)/3-1;
cout<<n-cnt<<endl;
return 0;
}