/*
	Nishant Singh
	nishant.ns19
*/
#include <bits/stdc++.h>
#include <functional> 
#include <iostream> 

// ******** Big Integer ********
// #include <boost/multiprecision/cpp_int.hpp>
// using namespace boost::multiprecision;
// #define ll1024  int1024_t
// ******** Big Integer ********

// ******** Using PBDS ********
// #include <ext/pb_ds/assoc_container.hpp> // Common file 
// #include <ext/pb_ds/tree_policy.hpp> 
// using namespace __gnu_pbds; 
// ******** Using PBDS ********

using namespace std;
#define ll long long
#define ld long double
#define pll pair<long long,long long>
#define pii pair<int,int>
#define vll vector<ll>
#define vec vector
#define setcount(x) __builtin_popcountll(x)
#define f first
#define s second
#define mp make_pair
#define REP(i,n) for(ll i=0;i<(n);i++)
#define FOR(i,a,b) for(ll i=(a);i<=(b);i++)
#define REV(i,a,b) for(ll i=(a);i>=(b);i--)
#define pb push_back
#define in insert
#define init(x,a) memset(x,a,sizeof(x))
#define all(c) c.begin(),c.end()
#define pq priority_queue
#define ffl fflush(stdout)
#define mset multiset
#define out(x) cout<<#x<<" = "<<" "<<x<<"\n";
#define ub upper_bound
#define lb lower_bound 
#define ln "\n"
#define Y "YES"
#define N "NO"
ll const mod=1e9 + 7;
ll const inf=2e18;

// ******** Using PBDS ********
// typedef tree<long long, null_type, less<long long>, rb_tree_tag, 
//              tree_order_statistics_node_update> 
//                 os; 
// ******** Using PBDS ********

inline ll add(ll a,ll b) 
{ 
	return (a%mod + b%mod + mod)%mod; 
}

inline ll mul(ll a,ll b) 
{ 
	return (a%mod * b%mod + mod)%mod; 
}

inline ll sub(ll a,ll b) 
{ 
	return (a%mod - b%mod + mod)%mod; 
}

ll gcd(ll a,ll b)
{
	if (b == 0) 
		return a; 
	return gcd(b, a % b);  
}

ll modexp(ll x, ll n){
	if(n==0){
		return 1;
	}
	else if(n&1){
		return (modexp((x*x)%mod, n/2)%mod * x%mod)%mod;
	}
	else{
		return (modexp((x*x)%mod, n/2)%mod);
	}
}

ll modinv(ll n)
{
	return modexp(n,mod-2);
}

// ******** GLOBAL VARIABLES ********


// ******** GLOBAL VARIABLES ********

void solve(){
	ll n;
	cin>>n;
	string s;
	cin>>s;
	vll r,g,b;
	REP(i,n)
	{
		if(s[i]=='R')
			r.pb(i);
		else if(s[i]=='G')
			g.pb(i);
		else if(s[i]=='B')
			b.pb(i);
	}
	ll ans=0;
	for(int i=0;i<n;i++)
	{
		if(s[i]=='R')
		{
			auto idx1=upper_bound(all(g),i);
			while(idx1!=g.end())
			{
				ll x=*idx1;
				ans=ans+(b.end()-upper_bound(all(b),x));
				if(binary_search(b.begin(), b.end(), x+x-i))
					ans--;
				idx1++;

			}
			idx1=upper_bound(all(b),i);
			while(idx1!=b.end())
			{
				ll x=*idx1;
				ans=ans+(g.end()-upper_bound(all(g),x));
				if(binary_search(g.begin(), g.end(), x+x-i))
					ans--;
				idx1++;
			}
		}
		else if(s[i]=='G')
		{
			auto idx1=upper_bound(all(r),i);
			while(idx1!=r.end())
			{
				ll x=*idx1;
				ans=ans+(b.end()-upper_bound(all(b),x));
				if(binary_search(b.begin(), b.end(), x+x-i))
					ans--;
				idx1++;
			}
			
			idx1=upper_bound(all(b),i);
			while(idx1!=b.end())
			{
				ll x=*idx1;
				ans=ans+(r.end()-upper_bound(all(r),x));
				if(binary_search(r.begin(), r.end(), x+x-i))
					ans--;
				idx1++;
			}

		}
		else
		{
			auto idx1=upper_bound(all(r),i);
			while(idx1!=r.end())
			{
				ll x=*idx1;
				ans=ans+(g.end()-upper_bound(all(g),x));
				if(binary_search(g.begin(),g.end(), x+x-i))
					ans--;
				idx1++;
			}
			idx1=upper_bound(all(g),i);
			while(idx1!=g.end())
			{
				ll x=*idx1;
				ans=ans+(r.end()-upper_bound(all(r),x));
				if(binary_search(r.begin(),r.end(), x+x-i))
					ans--;
				idx1++;
			}

		}

	}
	cout<<ans;


}  

int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	ll T=1;
	// cin>>T; 	
	for(int t=1;t<=T;t++)
	{
		// cout<<"Case #"<<t<<": ";
		solve();
	}
	return 0;
}

Measured memory_bytes: 3672