#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
void magic(){
int n; cin>>n;
string s; cin>>s;
if(n<=2){
cout<<0;
return ;
}
int mid = s.size() /2;
if(s[mid+1] == s[mid] || s[mid-1] == s[mid]) cout<<s.size() - 2;
else cout<<s.size() - 3;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie();
std::cout.tie();
int t = 1; //cin>>t;
while (t--)
magic();
}