#include<iostream>
#include<string.h>
using namespace std;
int n,fds[200001],f[100051][20][20];
void input()
{
memset(f,0xc0,sizeof(f));
f[0][0][0]=0;
cin>>n;
for(int i=0;i<n;i++)
{
char inchr;
cin>>inchr;
if(inchr=='M') fds[i]=1;
else if(inchr=='F') fds[i]=2;
else fds[i]=3;
for(int j=0;j<=15;j++)
{
for(int k=0;k<=15;k++)
{
if(f[i][j][k]>=0)
{
if(j==0) f[i+1][fds[i]][k]=max(f[i+1][fds[i]][k],f[i][j][k]+1);
else if(j/4==0)
{
if(j%4==fds[i]) f[i+1][j*4+fds[i]][k]=max(f[i+1][j*4+fds[i]][k],f[i][j][k]+1);
else f[i+1][j*4+fds[i]][k]=max(f[i+1][j*4+fds[i]][k],f[i][j][k]+2);
}
else
{
if(j/4==j%4&&j%4==fds[i]) f[i+1][(j%4)*4+fds[i]][k]=max(f[i+1][(j%4)*4+fds[i]][k],f[i][j][k]+1);
else if(j/4!=j%4&&j/4!=fds[i]&&j%4!=fds[i]) f[i+1][(j%4)*4+fds[i]][k]=max(f[i+1][(j%4)*4+fds[i]][k],f[i][j][k]+3);
else f[i+1][(j%4)*4+fds[i]][k]=max(f[i+1][(j%4)*4+fds[i]][k],f[i][j][k]+2);
}
if(k==0) f[i+1][j][fds[i]]=max(f[i+1][j][fds[i]],f[i][j][k]+1);
else if(k/4==0)
{
if(k%4==fds[i]) f[i+1][j][k*4+fds[i]]=max(f[i+1][j][k*4+fds[i]],f[i][j][k]+1);
else f[i+1][j][k*4+fds[i]]=max(f[i+1][j][k*4+fds[i]],f[i][j][k]+2);
}
else
{
if(k/4==k%4&&k%4==fds[i]) f[i+1][j][(k%4)*4+fds[i]]=max(f[i+1][j][(k%4)*4+fds[i]],f[i][j][k]+1);
else if(k/4!=k%4&&k/4!=fds[i]&&k%4!=fds[i]) f[i+1][j][(k%4)*4+fds[i]]=max(f[i+1][j][(k%4)*4+fds[i]],f[i][j][k]+3);
else f[i+1][j][(k%4)*4+fds[i]]=max(f[i+1][j][(k%4)*4+fds[i]],f[i][j][k]+2);
}
}
}
}
}
int ans=0;
for(int i=0;i<=15;i++)
{
for(int j=0;j<=15;j++) ans=max(ans,f[n][i][j]);
}
cout<<ans<<endl;
}
int main()
{
input();
return 0;
}

using namespace std;
int n,a[100010],ans,dp[2][4][4][4][4],point,pre;char c;
inline int Get_Char(){  
    char c;  
    do c=getchar(); while(c!='M'&&c!='F'&&c!='B');  
    switch(c){  
        case 'M':return 1;  
        case 'F':return 2;  
        case 'B':return 3;}}  
inline int score(int x,int y){  
    if(!x)return 1; 
    return x==y?1:2;}  
inline int score(int x,int y,int z){
    int temp=x*y*z;  
    switch(temp){  
        case 6:return 3;  
        case 1:return 1;
        case 8:return 1;
        case 27:return 1;  
        case 0:return score(y,z);  
        default: return 2;}}
int main(void){
    scanf("%d",&n);
    memset(dp,0xef,sizeof dp); 
    dp[0][0][0][0][0]=0;
    for(int i=1;i<=n;i++){
        int x=Get_Char();
        memset(dp+(i&1),0xef,sizeof(dp)>>1); 
        point=i&1;
        pre=~i&1;
        for(int i1=0;i1<=3;i1++)                                                                                                                                                                                                 
            for(int i2=(i1?1:0);i2<=3;i2++)
                for(int i3=0;i3<=3;i3++)
                    for(int i4=(i3?1:0);i4<=3;i4++)if(dp[~i&1][i1][i2][i3][i4]>=0) {
                        int q1=score(i1,i2,x);
                        int q2=score(i3,i4,x);
                        dp[point][i2][x][i3][i4]=max(dp[point][i2][x][i3][i4],dp[pre][i1][i2][i3][i4]+q1);
                        dp[point][i1][i2][i4][x]=max(dp[point][i1][i2][i4][x],dp[pre][i1][i2][i3][i4]+q2);}}
        for(int i1=0;i1<=3;i1++)
            for(int i2=(i1?1:0);i2<=3;i2++)
                for(int i3=0;i3<=3;i3++)
                    for(int i4=(i3?1:0);i4<=3;i4++)
                        ans=max(ans,dp[n&1][i1][i2][i3][i4]);
    cout<<ans;}