#include <bits/stdc++.h>
using namespace std;
#define ll long long
string s;
ll n,ans,r,g,b;
int main(){
    cin>>n>>s;
    for(int i=0;i<n;i++)
    {
    	if(s[i]=='R')r++;  if(s[i]=='G')g++;
    	if(s[i]=='B')b++;
	}
	ans=r*g*b;
    for(int i=0;i<n;i++)
      for(int j=i+1;j<n,2*j-i<n;j++)
      {
      	if(s[i]!=s[j]&&s[j]!=s[2*j-i]&&s[i]!=s[2*j-1])
      	  ans--;
	  }
	cout<<ans;
	return 0;
}
