#include "bits/stdc++.h"
using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<char> vc;
typedef vector<vc> vvc;
typedef vector<pii> vpii;
typedef vector<pair<ll,ll> > vpll;
typedef vector<vector<pair<ll,ll> > > vvpll;
typedef vector<bool> vb;
typedef map<int,int> mii;
typedef map<char,int> mci;
typedef map<ll,ll> mll;

#define FIO ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define all(x) x.begin() , x.end()
#define pb push_back
#define bs binary_search
#define lb lower_bound
#define ub upper_bound
#define mp make_pair
#define F first
#define S second
#define left (node << 1)
#define right (node << 1) + 1
// #define mod 998244353
#define mod 1000000007 

#define trace1(x)                       cerr<<#x<<": "<<x<<endl
#define trace2(x, y)                    cerr<<#x<<": "<<x<<" | "<<#y<<": "<<y<<endl
#define trace3(x, y, z)                 cerr<<#x<<": " <<x<<" | "<<#y<<": "<<y<<" | "<<#z<<": "<<z<<endl
#define trace4(x, y, z , t)             cerr<<#x<<": " <<x<<" | "<<#y<<": "<<y<<" | "<<#z<<": "<<z<<" | "<<#t<<": "<<t<<endl
#define trace5(x, y, z , t , u)         cerr<<#x<<": " <<x<<" | "<<#y<<": "<<y<<" | "<<#z<<": "<<z<<" | "<<#t<<": "<<t<<" | "<<#u<<": "<<u<<endl
#define trace6(x, y, z , t , u , v)     cerr<<#x<<": " <<x<<" | "<<#y<<": "<<y<<" | "<<#z<<": "<<z<<" | "<<#t<<": "<<t<<" | "<<#u<<": "<<u<<" | "<<#v<<": "<<v<<endl

#define repa(i,sta,end,inc) for(int i = sta ; i <= end ; i += inc)
#define repb(i,sta,end,inc) for(int i = sta ; i >= end ; i -= inc)

ll power(ll x , ll y , ll z){ll res = 1;x %= z;while(y){if(y&1){res = res * x % z;}x = x*x % z;y /= 2;}return res%z;}
ll gcd(ll a , ll b){return (b == 0 ? a : gcd(b , a % b));}

const int N = 2 * 100000 + 1;
const int inf = (1<<30);

void solve(){
    int n;
    string s;
    cin >> n >> s;
    vi r,g,b;
    repa(i,0,n-1,1){
        if(s[i] == 'R'){
            r.pb(i);
        }
        else if(s[i] == 'G'){
            g.pb(i);
        }
        else {
            b.pb(i);
        }
    }
    ll ans = 0;
    repa(i,0,r.size()-1,1){
        int ri = r[i];
        int id = ub(all(g),ri)-g.begin();
        if(id != g.size()){
            repa(j,id,g.size()-1,1){
                int gj = g[j];
                int id_ = ub(all(b),gj)-b.begin();
                if(id_ != b.size()){
                    ans += b.size() - id_;
                    if(bs(all(b) , 2*gj-ri))ans--;
                }
            }
        }
    }
    repa(i,0,r.size()-1,1){
        int ri = r[i];
        int id = ub(all(b),ri)-b.begin();
        if(id != b.size()){
            repa(j,id,b.size()-1,1){
                int bj = b[j];
                int id_ = ub(all(g),bj)-g.begin();
                if(id_ != g.size()){
                    ans += g.size() - id_;
                    if(bs(all(g) , 2*bj-ri))ans--;
                }
            }
        }
    }
    repa(i,0,g.size()-1,1){
        int gi = g[i];
        int id = ub(all(r),gi)-r.begin();
        if(id != r.size()){
            repa(j,id,r.size()-1,1){
                int rj = r[j];
                int id_ = ub(all(b),rj)-b.begin();
                if(id_ != b.size()){
                    ans += b.size() - id_;
                    if(bs(all(b) , 2*rj-gi))ans--;
                }
            }
        }
    }
    repa(i,0,g.size()-1,1){
        int gi = g[i];
        int id = ub(all(b),gi)-b.begin();
        if(id != b.size()){
            repa(j,id,b.size()-1,1){
                int bj = b[j];
                int id_ = ub(all(r),bj)-r.begin();
                if(id_ != r.size()){
                    ans += r.size() - id_;
                    if(bs(all(r) , 2*bj-gi))ans--;
                }
            }
        }
    }
    repa(i,0,b.size()-1,1){
        int bi = b[i];
        int id = ub(all(g),bi)-g.begin();
        if(id != g.size()){
            repa(j,id,g.size()-1,1){
                int gj = g[j];
                int id_ = ub(all(r),gj)-r.begin();
                if(id_ != r.size()){
                    ans += r.size() - id_;
                    if(bs(all(r) , 2*gj-bi))ans--;
                }
            }
        }
    }
    repa(i,0,b.size()-1,1){
        int bi = b[i];
        int id = ub(all(r),bi)-r.begin();
        if(id != r.size()){
            repa(j,id,r.size()-1,1){
                int rj = r[j];
                int id_ = ub(all(g),rj)-g.begin();
                if(id_ != g.size()){
                    ans += g.size() - id_;
                    if(bs(all(g) , 2*rj-bi))ans--;
                }
            }
        }
    }
    cout << ans << endl;
}


int main(){
    FIO;
    int T = 1;
    // cin >> T;
    repa ( i , 1 , T , 1){
        solve();
    }
    return 0;
}
