#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cctype>
#include <cassert>
#include <climits>
#include <string>
#include <bitset>
#include <cfloat>
#include <random>
#include <iomanip>
#include <unordered_set>
#pragma GCC optimize("Ofast")
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef vector<pair<int,int> > vpii;
typedef vector<vector<int> > vvi;
typedef vector<vector<char> > vvc;
typedef vector<vector<string> > vvs;
typedef vector<vector<ll> > vvll;
typedef map<int, int> mii;
typedef set<int> si;
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define irep(it, stl) for(auto it = stl.begin(); it != stl.end(); it++)
#define drep(i,n) for(int i = (n) - 1; i >= 0; --i)
#define fin(ans) cout << (ans) << '\n'
#define STLL(s) strtoll(s.c_str(), NULL, 10)
#define mp(p,q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
#define itn int
// #define endl '\n';
#define fi first
#define se second
#define NONVOID [[nodiscard]]
const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
template <class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;} return 0;}
template <class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;} return 0;}
template<class T> inline void dump(T &v){irep(i, v){cout<<*i<<((i==--v.end())?'\n':' ');}}
inline string getline(){string s; getline(cin,s); return s;}
inline void yn(const bool b){b?fin("yes"):fin("no");}
inline void Yn(const bool b){b?fin("Yes"):fin("No");}
inline void YN(const bool b){b?fin("YES"):fin("NO");}
struct io{io(){ios::sync_with_stdio(false);cin.tie(0);}};
const int INF = INT_MAX;
const ll LLINF = 1LL<<60;
const ll MOD = 1000000007;
const double EPS = 1e-9;

// vector vの中のn以下の数で最大のものを返す
int bs(vector<int> &v, int x){
    int ok = -1; //これがx以下 
    int ng = v.size(); //x以上 
    // 問題によってokとngを入れ替える
    while(abs(ok - ng) > 1){
        int mid = (ok + ng)/2;
        if(v[mid] <= x) ok = mid;
        else ng = mid;
    }
    return ok;
}

int main() {
    
    int n;
    string s;
    cin>>n>>s;
    vvi v(3);
    ll ans=0;
    vi w(n);
    rep(i,n){
        if(s[i]=='R')w[i]=0;
        else if(s[i]=='G')w[i]=1;
        else if(s[i]=='B')w[i]=2;
    }
    rep(i,n)v[w[i]].pb(i);
    for(int i=0;i<n;i++){
        for(int j=i+1;j<n;j++){
            if(w[i]==w[j])continue;
            int last;
            if(min(w[i],w[j])==0&&max(w[i],w[j])==1)last=2;
            else if(min(w[i],w[j])==1&&max(w[i],w[j])==2)last=0;
            else if(min(w[i],w[j])==0&&max(w[i],w[j])==2)last=1;
            int tmp=0;
            int pos=bs(v[last],j)+1;
            // cout<<i<<" "<<j<<" "<<pos<<" ";
            if(pos==v[last].size())tmp+=0;
            else{
                tmp+=v[last].size()-pos;
                if(j+(j-i)<w.size()&&w[j+(j-i)]==last)tmp--;
                // cout<<w[j+(j-i)]<<" "<<last<<" ";
            }
            // cout<<tmp<<endl;
            ans+=tmp;
        }
    }
    fin(ans);

}




Measured memory_bytes: 3640