#include<iostream>
#include<iomanip>
#include<cmath>
#include<algorithm>
#include<string>
#include<cstring>
#include<queue>
#include<deque>
#include<vector>
#include<stack>
#include<set>
#include<map>
#include<deque>
#include<fstream>
using namespace std;
int n,cnt,ans=1;
string s;
int main(){
    cin>>n;
    cin>>s;
    s=" "+s;
    for(int i=1;i<=n;i++){
        if(s[i]!='1'){
            continue;
        }
        if(s[i]=='1'){
            int cnt1=0,cnt2=0;
            while(s[i]=='1'&&i<n){
                i++;
                cnt1++;
            }
            if(s[i]!='/'){
                continue;
            }i++;
            while(s[i]=='2'&&i<=n){
                i++;
                cnt2++;
            }
            ans=max(ans,min(cnt1,cnt2)*2+1);
        }
    }
    cout<<ans<<endl;
    return 0;
}