// Problem : D - RGB Triplets
// Contest : AtCoder Beginner Contest 162
// URL : https://atcoder.jp/contests/abc162/tasks/abc162_d
// Memory Limit : 1024 MB
// Time Limit : 2000 ms
// Powered by CP Editor (https://github.com/cpeditor/cpeditor)

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>

#define ll long long
#define pb push_back
#define f first
#define s second
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define D(x) cerr << #x << " is " << (x) << "\n";
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>

#define ll long long
#define pb push_back
#define f first
#define s second
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define ios ios_base::sync_with_stdio(false);cin.tie(NULL)
#define D(x) cerr << #x << " is " << (x) << "\n";
#define ld long double
#define li __int128

using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>; ///find_by_order(),order_of_key()
template<class T1, class T2> ostream& operator<<(ostream& os, const pair<T1,T2>& a) { os << '{' << a.f << ", " << a.s << '}'; return os; }
template<class T> ostream& operator<<(ostream& os, const vector<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const deque<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T1,class T2> ostream& operator<<(ostream& os, const map<T1,T2>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T1, class T2> istream& operator>>(istream& is,pair<T1,T2>& a) {is>>a.f>>a.s;return is;}
template<class T> istream& operator>>(istream& is,vector<T>& a) {for(auto &p:a)is>>p;return is;}
//istream& operator>>(istream& is,__int128& a){string s;is>>s;a=0;for(auto p:s)a=a*10+p-'0';return is;}
//ostream& operator<<(ostream& os,__int128 a){bool neg=false;if(a<0)neg=true,a*=-1;ll high=(a/(__int128)1e18);ll low=(a-(__int128)1e18*high);string res;if(neg)res+='-';if(high>0){res+=to_string(high);string temp=to_string(low);res+=string(18-temp.size(),'0');res+=temp;}else res+=to_string(low);os<<res;return os;}

int main()
{
	int n;
	scanf("%i",&n);
	string s;
	cin >> s;
	vector<vector<int> > cnt(3,vector<int>(n+1));
	for(auto &p:s){
		if(p=='R')
			p=0;
		if(p=='G')
			p=1;
		if(p=='B')
			p=2;
	}
	for(int i=n-1;i>=0;i--){
		for(int j=0;j<3;j++)
			cnt[j][i]+=cnt[j][i+1];
		cnt[s[i]][i]++;
	}
	ll sol=0;
	for(int i=0;i<n;i++){
		for(int j=i+1;j<n;j++){
			if(s[i]==s[j])
				continue;
			int p=j+(j-i);
			if(s[i]!=0&&s[j]!=0){
				if(p<n&&s[p]==0)
					sol+=cnt[0][j]-1;
				else
					sol+=cnt[0][j];
			}
			if(s[i]!=1&&s[j]!=1){
				if(p<n&&s[p]==1)
					sol+=cnt[1][j]-1;
				else
					sol+=cnt[1][j];
			}
			if(s[i]!=2&&s[j]!=2){
				if(p<n&&s[p]==2)
					sol+=cnt[2][j]-1;
				else
					sol+=cnt[2][j];
			}
		}
	}
	cout << sol << endl;
	return 0;
}


Measured memory_bytes: 3756