#include<bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
 
#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
 
#define start_routine() int begtime = clock();
#define end_routine() int endtime = clock(); cerr << endl << "Time elapsed: " << (endtime - begtime)*1000/CLOCKS_PER_SEC << " ms"; return 0
#define speed() cin.tie(0), cout.tie(0), ios_base::sync_with_stdio(false)
// #define exit(a, b) return cout << a, b;
 
// debugger
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1>
void __f(const char* name, Arg1&& arg1){
    cout << name << " : " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args){
    const char* comma = strchr(names + 1, ',');cout.write(names, comma - names) << " : " << arg1<<" | ";__f(comma+1, args...);
}
#define debug(stuff) cout << #stuff << ": " << stuff <<endl
#define debugc(stuff) cout << #stuff << ": "; for(auto x: stuff) cout << x << " "; cout << endl;
// 
 
#define loop(i,a,b) for(ll i=a;i<b;i++)
#define all(v) v.begin(), v.end() 
 
#define print(stuff) cout << stuff << endl
#define printc(stuff) for(auto x: stuff) cout << x << " "; cout << endl;
#define printPrec(stuff) cout << fixed << setprecision(15) << stuff << endl;
#define len length
#define ret0 return 0
#define ret return 
 
 
#define ll long long
#define ld long double
#define fi first
#define endl '\n'
#define se second
#define pb push_back
#define mp make_pair
#define lb lower_bound
#define ub upper_bound
#define fill(ar, x) memset(ar, x, sizeof ar)
 
#define vl vector<ll> 
#define sl set<ll>
#define pll pair<ll, ll>
#define mll map<ll, ll> 
#define pq priority_queue<ll>
 
// typedef tree<ll,null_type,less<ll>,rb_tree_tag,
// tree_order_statistics_node_update> indexed_set;
 
#define inf (long long int) 1e18
#define eps 0.000001
#define mod 1000000007
#define mod1 998244353
#define MAXN (ll)2e5+5
#define N (1ll<<10)

void solve(){
    ll n;
    cin>>n;
    string s;
    cin>>s;
    ll r[n] = {0}, g[n] = {0}, b[n] = {0};
    r[n-1] = (s[n-1] == 'R')?1:0;
    b[n-1] = (s[n-1] == 'B')?1:0;
    g[n-1] = (s[n-1] == 'G')?1:0;
    for(ll i=n-2; i>=0; i--){
        // trace(i, s[i]);
        if(s[i] == 'R'){
            // print("pp");
            r[i] = r[i+1]+1, g[i] = g[i+1], b[i] = b[i+1];
        }
        if(s[i] == 'G'){
            r[i] = r[i+1], g[i] = g[i+1]+1, b[i] = b[i+1];
        }
        if(s[i] == 'B'){
            r[i] = r[i+1], g[i] = g[i+1], b[i] = b[i+1]+1;
        }
    }
    // printc(r);
    // printc(b);
    ll ans = 0;
    for(ll i=0; i<n-2; i++){
        for(ll j=i+1; j<n-1; j++){
            if(s[i] != s[j]){
                if(min(s[i], s[j]) == 'B' && max(s[i], s[j]) == 'R'){
                    ans += g[j+1];
                    if(2*j - i < n && s[2*j-i] == 'G') ans--;
                }
                if(min(s[i], s[j]) == 'G' && max(s[i], s[j]) == 'R'){
                    ans += b[j+1];
                    if(2*j - i < n && s[2*j-i] == 'B') ans--;
                }
                if(min(s[i], s[j]) == 'B' && max(s[i], s[j]) == 'G'){
                    ans += r[j+1];
                    if(2*j - i < n && s[2*j-i] == 'R') ans--;
                }
            }
        }
    }
    print(ans);
}
 
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    #ifndef ONLINE_JUDGE
        start_routine();
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    #endif
 
    ll t = 1;
    // cin>>t;
    while(t--){
        solve();
    }
        
    #ifndef ONLINE_JUDGE
        end_routine();
    #endif
}


Measured memory_bytes: 3708