#include <bits/stdc++.h>
#define NMAX 100001
#define int long long
#define pb push_back
#define eb emplace_back
#define MOD 1000000007
#define nl '\n'
#define INF 1000000007
#define LLONG_MAX 9223372036854775807
#define pii pair<int,int>
#define tpl tuple<int,int,int,int>
//#pragma GCC optimize("O3")
using namespace std;
ifstream fin("aib.in");
ofstream fout("aib.out");
/*
*
*
----------------DEMONSTRATION-------------------
MBMFFB
mine1 mine2
MBF MFB
1+2+3=6 1+2+3=6
MBMFFB
---------------------END------------------------
*/
/*-------------Initialize------------*/
int n;
string s;
struct dinamica{
int ind1,ind2,ind3,val;
};
dinamica dp[3][3][NMAX];// dp[type][mine][i]->food from i will go to mine[type]
int v[NMAX];
vector<int>ind(NMAX);
int check(int ind,int t_f,int mine_f,int ind_f)
{
map<int,int>mp;
if(v[dp[t_f][mine_f][ind_f].ind3])
mp[v[dp[t_f][mine_f][ind_f].ind3]]++;
if(v[dp[t_f][mine_f][ind_f].ind2])
mp[v[dp[t_f][mine_f][ind_f].ind2]]++;
if(v[ind])
mp[v[ind]]++;
if(mp.size()==3)
return 3;
else if(mp.size()==2)
return 2;
else
return 1;
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin>>n;
cin>>s;
v[0]=0;
for(int i=1;i<=n;++i)
{
if(s[i-1]=='M')
v[i]=1;
else if(s[i-1]=='F')
v[i]=2;
else
v[i]=3;
}
dp[1][1][1].ind3=1;
dp[1][1][1].val=1;
dp[2][2][1].val=1;
dp[2][2][1].ind3=1;
for(int i=2;i<=n;++i)
{
if(dp[1][1][i-1].val+check(i,1,1,i-1)>dp[2][1][i-1].val+check(i,2,1,i-1))
{
dp[1][1][i].val=dp[1][1][i-1].val+check(i,1,1,i-1);
dp[1][1][i].ind1=dp[1][1][i-1].ind2;
dp[1][1][i].ind2=dp[1][1][i-1].ind3;
dp[1][1][i].ind3=i;
}
else
{
dp[1][1][i].val=dp[2][1][i-1].val+check(i,2,1,i-1);
dp[1][1][i].ind1=dp[2][1][i-1].ind2;
dp[1][1][i].ind2=dp[2][1][i-1].ind3;
dp[1][1][i].ind3=i;
}
if(dp[2][2][i-1].val+ check(i,2,2,i-1)>dp[1][2][i-1].val+check(i,1,2,i-1))
{
dp[2][2][i].val=dp[2][2][i-1].val+ check(i,2,2,i-1);
dp[2][2][i].ind1=dp[2][2][i-1].ind2;
dp[2][2][i].ind2=dp[2][2][i-1].ind3;
dp[2][2][i].ind3=i;
}
else
{
dp[2][2][i].val=dp[1][2][i-1].val+check(i,1,2,i-1);
dp[2][2][i].ind1=dp[1][2][i-1].ind2;
dp[2][2][i].ind2=dp[1][2][i-1].ind3;
dp[2][2][i].ind3=i;
}
if(dp[2][1][i-1].val>dp[1][1][i-1].val)
{
dp[2][1][i]=dp[2][1][i-1];
}
else
{
dp[2][1][i]=dp[1][1][i-1];
}
if(dp[1][2][i-1].val>dp[2][2][i-1].val)
{
dp[1][2][i]=dp[1][2][i-1];
}
else
{
dp[1][2][i]=dp[2][2][i-1];
}
}
// for(int i=1;i<=n;++i)
// {
// cout<<i<<": "<<nl;
// cout<<"1->1"<<" val:"<<dp[1][1][i].val<<" ind1:"<<dp[1][1][i].ind1<<" ind2:"<<dp[1][1][i].ind2<<" ind3:"<<dp[1][1][i].ind3<<nl;
// cout<<"2->2"<<" val:"<<dp[2][2][i].val<<" ind1:"<<dp[2][2][i].ind1<<" ind2:"<<dp[2][2][i].ind2<<" ind3:"<<dp[2][2][i].ind3<<nl;
// cout<<"1->2"<<" val:"<<dp[1][2][i].val<<" ind1:"<<dp[1][2][i].ind1<<" ind2:"<<dp[1][2][i].ind2<<" ind3:"<<dp[1][2][i].ind3<<nl;
// cout<<"2->1"<<" val:"<<dp[2][1][i].val<<" ind1:"<<dp[2][1][i].ind1<<" ind2:"<<dp[2][1][i].ind2<<" ind3:"<<dp[2][1][i].ind3<<nl;
//
// cout<<nl<<nl;
//
// }
int ans=max({dp[1][1][n].val,dp[2][2][n].val,dp[1][2][n].val,dp[2][1][n].val});
cout<<ans;
return 0;
}
