#include <iostream>
#include <cstring>
#define ll long long
#define G 'G'
#define H 'H'

using namespace std;

int main()
{
	//freopen("mine.txt","w",stdout);
	//freopen("data.txt","r",stdin);
	ll n;
	ll ans = 0;
	string str;
	cin >> n >> str;
	for(ll i = 0; i < n - 2; i ++)
	{
		ll g = (str[i] == G) + (str[i + 1] == G) + (str[i + 2] == G);
		ll h = 3 - g;
		if(g == 1)
		{
			int  ii = i+2;
			do
			{
				//cout<<i<<" "<<ii<<endl;
				ans ++;
			}while(str[++ii] != G && ii < n);
		}
		if(h == 1)
		{
			int  ii = i+2;
			do
			{
				//cout<<i<<" "<<ii<<endl;
				ans ++;
			}while(str[++ii] != H && ii < n );
		}
	}
	cout << ans;
}