#include<bits/stdc++.h>
using namespace std;
int n,s,g,ans,t1,t2;
char a[10005];
int main(){
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        cin>>a[i];
        if(a[i]=='G') g++;
        if(a[i]=='S') s++;
    }
    for(int i=1;i<=g;i++)
    { 
        if(a[i]!='G') ans++;
        if(a[i]=='S') t1++;
    }
    for(int i=g+1;i<=g+s;i++)
    { 
        if(a[i]!='S') ans++;
        if(a[i]=='G') t2++;
    }
    cout<<ans-min(t1,t2);
    return 0;
}

/**************************************************************
	Problem: 1578
	User: admin
	Language: C++
	Result: Accepted
	Time:50 ms
	Memory:2084 kb
****************************************************************/