/*---> 13 April 2020 <--- > 00:00:00 <---*/
// #pragma GCC optimize("Ofast")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
// #pragma GCC optimize("unroll-loops")
// #pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("O3")
//#pragma GCC target ("sse4")
#include <bits/stdc++.h>
//#include <ext/pb_ds/tree_policy.hpp>
//#include <ext/pb_ds/assoc_container.hpp>
//using namespace __gnu_pbds;
using namespace std;
//template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;
#define int long long
#define F first
#define S second
#define mod 1000000007
#define inf (int)1e18+5
#define sz(x) (int)x.size()
#define PI 3.141592653589793238510
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define __ ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define vi vector<int>
#define vpii vector<pair<int,int> > 
#define vvi vector<vector<int> >
#define PRINT_TIME cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s." <<endl;
#define sim template < class c
#define ris return * this
#define dor > debug & operator <<
#define eni(x) sim > typename   enable_if<sizeof dud<c>(0) x 1, debug&>::type operator<<(c i) {
sim > struct rge { c b, e; };
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c* x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
~debug() { cerr << endl; }
eni(!=) cerr << boolalpha << i; ris; }
eni(==) ris << range(begin(i), end(i)); }
sim, class b dor(pair < b, c > d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
sim dor(const c&) { ris; }
#endif
};
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
typedef long double ld;
typedef pair<int,int> pii;
///////////////////////////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////////////////////////
const int N=1e5+5;
struct custom_hash{
    static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
}
size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
 }
};
int val(char cc){
    if(cc=='R')
        return 1;
    else if(cc=='G')
        return 2;
    return 3;
}
int32_t main(){__
    int n;
    cin>>n;
    string s;
    cin>>s;
    int ans=0;

    for(int i=0;i<n;i++){
        unordered_map<int,int,custom_hash> ss[4];
        int cur=val(s[i]);
        for(int j=0;j<i;j++){
            int o=val(s[j]);
            if(cur!=o){
                ss[o][i-j]++;
            }
        }
        vi vv(4);
        for(int j=1;j<=3;j++){
            if(cur==j)
                continue;
            for(auto k:ss[j]){
                vv[j]+=k.second;
            }
        }
        for(int j=i+1;j<n;j++){
            int o=val(s[j]);
            ans+=(vv[o^cur]-ss[o^cur][j-i]);
        }

        // debug()<< imie(ans) imie(i) imie(ss[1]) imie(ss[2]);
    }
    cout<<ans<<"\n";
return 0;
}

Measured memory_bytes: 3768