#include <iostream>
#include <string>
using namespace std;
int main()
{
    int a[1000];
    int n,i,k;
    char Name;
    cin>>n;
    string B;
    k=0;
    for (i=0;i<n;i++){
        cin>>B;
        Name=B[0];
            if(Name=='A' or Name=='P' or Name=='O' or Name=='R') {a[i]=1;}
            else {if(Name=='B' or Name=='M' or Name=='S') {a[i]=2;}
                else {a[i]=3;};
                }
        }
    k=a[0]-1;

    for (i=1;i<n;i++){
        if (a[i-i]<a[i]){ k=k+a[i]-a[i-1];}
        else { k=k+a[i-1]-a[i];}

        }
    cout<<k;
        return 0;

}