//----AUTHOR:kkdrummer----/
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include<ext/rope>
using namespace __gnu_cxx;
using namespace __gnu_pbds;
using namespace std;
typedef    long long   ll;
typedef    long double   ld;
typedef    complex<ld>   P;
#define    X   real()
#define    Y   imag()
ld restant(P p){return abs(p);}
//polar(x,y) mag=l,arg=y
//typedef    unordered_set<ll>   usll;
//typedef    unordered_multiset<ll>   umsll;
typedef    multiset<ll>   msll;
typedef    set<ll>   sll;
typedef    vector<ll>   vll;
typedef    pair<ll,ll>   pll;
typedef    vector<pair<ll,ll> >   vpll;
typedef    priority_queue<ll>   pqll;
typedef    vector<int>   vi;
typedef    set<int>   si;
typedef    multiset<int>   msi;
//typedef    unordered_multiset<int>   umsi;
//typedef    unordered_set<int>   usi;
typedef     pair<int,int>   pi;
typedef    vector<pair<int,int> >   vpi;
typedef    vector<pair<double,double> >   vpd;
typedef    pair<double,double>   pd;
typedef    priority_queue<int>   pqi;
typedef    tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update>   ind_set;
typedef    tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>   ind_setll;
#define    in   insert
#define    fi   first
#define    se   second
#define    pb   push_back
#define    mp   make_pair
#define    be   begin
#define    en   end
#define    itr   iterator
#define io ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define    mo   1000000007
#define    inf   1000000000000000001
#define    ninf   -1000000000000000001
#define    ima   1000000001
#define    imi   -1000000001
#define    oncnt    __builtin_popcount
#define    zerobegin   __builtin_clz
#define    zeroend   __builtin_ctz
#define    parity   __builtin_parity
#define all(x) x.be(),x.en()
#define    eps   1e-9
const    ld   PI=3.14159265359;
inline ll modpow(ll x,ll n){if(n==0)return 1;if(n==1)return(x%mo);ll u=(modpow(x,n/2));u=(u*u)%mo;if(n%2!=0)u=(u*x%mo)%mo;return u;}
inline ll modinv(ll x){return modpow(x,mo-2);}
inline ll mmul(ll a,ll b){    if(a>=mo)a=a%mo;if(b>=mo)b=b%mo;if(a*b>=mo)return(a*b)%mo;return(a*b);}
inline ll madd(ll a, ll b){if(a>=mo)a=a%mo;if(b>=mo)b=b%mo;if(a+b>=mo)return(a+b)%mo;return(a+b);}
inline ll msub(ll a, ll b){if(a>=mo)a=a%mo;if(b>=mo)b=b%mo;return((a-b+mo)%mo);}
inline ll mdiv(ll a,ll bb){if(a>=mo)a=a%mo;ll b=modinv(bb);if(b>=mo)b=b%mo;if(a*b>=mo)return(a*b)%mo;return(a*b);}
inline ll gcd(ll a,ll b){return __gcd(a,b);}

int main()
{
io
int testcases=1;//cin>>testcases;
while(testcases--)
{	
int n;
cin>>n;
string s;
cin>>s;
ll r[n+1]={0},g[n+1]={0},b[n+1]={0};
for(int i=0;i<n;i++)
{
	if(s[i]=='R')
	r[i]++;
	else if(s[i]=='G')
	g[i]++;
	else
	b[i]++;
	
}

for(int i=1;i<=n;i++)
{
	r[i]+=r[i-1];
	g[i]+=g[i-1];
	b[i]+=b[i-1];
}


ll ans=0;

for(int i=0;i<n;i++)
{
	for(int j=i+1;j<n;j++)
	{if(s[i]!=s[j])
	{
		int l=j-i;
		int k=min(n,j+l);
		ll an;
		set<char> ss;
		ss.insert(s[i]);
		ss.insert(s[j]);
		if(ss.find('R')==ss.end())
		{
			an=r[k-1]-r[j];
			an+=(r[n-1]-r[k]);
		}
		else if(ss.find('G')==ss.end())
		{
				an=g[k-1]-g[j];
			an+=(g[n-1]-g[k]);
		}
		else
		{
			an=b[k-1]-b[j];
			an+=(b[n-1]-b[k]);
		}
		ans+=an;
	}
	}
}

cout<<ans;

}return 0;}

Measured memory_bytes: 3696