/*
    Ujjawal Pabreja
*/
#include <bits/stdc++.h> 
#include <functional> 
using namespace std;
using ll = long long;
using ld = long double;
#define speed_cubing    ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define rep(i,a)        for(ll i = 0 ; i < a ; i++)
#define repe(i,a,b)     for(ll i = a ; i < b ; i++)
#define bac(i,a)        for(ll i = a ; i >= 0 ; i--)
#define bace(i,a,b)     for(ll i = a ; i >= b ; i--)
#define pb              push_back
#define mp              make_pair
#define in              insert
#define ff              first
#define ss              second
#define vv              vector
#define vll             vector <ll>
#define pll             pair <ll,ll>
#define vpll            vector <pll>
#define umap            unordered_map
#define uset            unordered_set
#define mset            multiset
#define pqueue          priority_queue
#define setbit(x)       __builtin_popcountll(x)
#define init(c,a)       memset(c,a,sizeof(c))
#define all(c)          c.begin(),c.end()
#define sz(c)           (ll)c.size()
#define lb              lower_bound
#define ub              upper_bound
#define maxe            *max_element
#define mine            *min_element
#define gcd(a,b)        __gcd(a,b)
#define rev             reverse
#define Y				"YES"
#define N 				"NO"
#define nl              "\n"
#define debug(x)        cout << #x << " : " << x << nl;
const ll inf = 1e18;  
const ll mod = 1e9 + 7;
const ll MOD = 998244353;
const ll MAX = 2e5 + 1;

// ====== int_1024t begins ======
// #include <boost/multiprecision/cpp_int.hpp>
// using namespace boost::multiprecision;
// ====== int_1024t ends ======

// ====== pbds begins ======
// #include <ext/pb_ds/assoc_container.hpp> 
// #include <ext/pb_ds/tree_policy.hpp>
// using namespace __gnu_pbds;
// typedef tree<pair<int,int>, null_type, less<pair<int,int>>, rb_tree_tag, 
//         tree_order_statistics_node_update> 
//         pbds; 
// ====== pbds ends ======

// ====== Useful functions begin ======
inline ll add(ll a,ll b) {return ((a%mod)+(b%mod))%mod;}
inline ll sub(ll a,ll b) {return ((a%mod)-(b%mod)+mod)%mod;}
inline ll mul(ll a,ll b) {return ((a%mod)*(b%mod))%mod;}
ll pwr(ll x,ll n){
    if(!n) return 1;
    if(n&1) return mul(x, pwr(mul(x,x),(n-1)/2));
    else return pwr(mul(x,x),n/2);
}
ll modinv(ll n){ 
    return pwr(n,mod - 2); 
}
// ====== Useful functions end ======
 
// ====== Variables begin ======

// ====== Variables end ======
void speed_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{
            b.pb(i);
        }
    }
    ll ans = 0;
    ll z = sz(r), y = sz(g), x = sz(b);
    rep(i,z){
        ll l = lb(all(g), r[i]) - g.begin();
        rep(j,y){
            ll diff = abs(g[j] - r[i]);
            ll chk = max(g[j], r[i]) + diff;
            ans += x;
            if(binary_search(all(b),chk)){
                ans--;
            }
            if(min(g[j], r[i]) >= diff){
                chk = min(g[j], r[i]) - diff;
                if(binary_search(all(b),chk)){
                    ans--;
                }
            }
            if(!(diff&1)){
                chk = min(g[j], r[i]) + diff/2;
                if(binary_search(all(b),chk)){
                    ans--;
                }
            }
        }
    }
    cout << ans;
}
int main()
{
    speed_cubing;
    ll test_cases = 1;
    // cin >> test_cases;
    rep(i,test_cases){
        // cout << "Case #" << i + 1 << ": ";
        speed_solve();
    }
    return 0;
}

Measured memory_bytes: 3700