#include<bits/stdc++.h>
using namespace std;
/*#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
/*template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
*/typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll,ll> pl;
typedef pair<int,int> pii;

#define int ll
#define LOCAL 0
#define dbg(x) cout << #x << " is " << x << "\n"
#define gll(x) scanf("%d",&x)
#define gll2(x,y) scanf("%d%d",&x,&y)
#define gll3(x,y,z) scanf("%d%d%d",&x,&y,&z)
#define gllarr(arr,n) f(i,n) gll(arr[i]);
#define sz(x) ((int)x.size())
#define s(x) sort(x.begin(),x.end())
#define all(v) v.begin(),v.end()
#define rs(v) { s(v) ; r(v) ; }
#define r(v) {reverse(all(v));}
#define pb push_back
#define f(i,n) for(int i=0;i<n;i++)
#define fr(i,n) for(int i=n-1;i>=0;i--)
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define repr(i,a,b) for(int i=a;i>=b;i--)

const ll mod = (ll)1e9 + 7;
const ll inf = (ll)1e16;
const ld eps = 1e-12;
const ll N = (int)3e5 + 5;
const ll LOGN = 19;
const ld PI = 3.14159265358979323846;
inline ll mul(ll a, ll b, ll m = mod) { return (ll)(a * b) % m;}
inline ll add(ll a, ll b, ll m = mod) { a += b; if(a >= m) a -= m; if(a < 0) a += m; return a;}
inline ll power(ll a, ll b, ll m = mod) { if(b == 0) return 1; if(b == 1) return (a % m); ll x = power(a, b / 2, m); x = mul(x, x, m); if(b % 2) x = mul(x, a, m); return x;}

void solve() {
    int n;
    cin>>n;
    string s;
    cin>>s;
    vector<int> rsuff(n, 0), bsuff(n, 0), gsuff(n, 0);
    for(int i = n - 2; i >= 0; i--) {
        rsuff[i] = rsuff[i + 1];
        bsuff[i] = bsuff[i + 1];
        gsuff[i] = gsuff[i + 1];
        if(s[i + 1] == 'R') rsuff[i]++;
        else if(s[i + 1] == 'G') gsuff[i]++;
        else bsuff[i]++;
    }
    int ans = 0;
    f(i, n - 2) {
        for(int j = i + 1; j < n; j++){
            if(s[i] == s[j]) continue;
            char col = ('R' ^ 'G' ^ 'B' ^ s[i] ^ s[j]);
            if(col == 'R') {
                ans += rsuff[j];
                if(j + j - i < n && s[j + j - i] == 'R') ans--;
            }
            else if(col == 'B') {
                ans += bsuff[j];
                if(j + j - i < n && s[j + j - i] == 'B') ans--;
            }
            else {
                ans += gsuff[j];
                if(j + j - i < n && s[j + j - i] == 'G') ans--;
            }
        }
    }
    cout<<ans;
}

int32_t main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    if (LOCAL) {
        freopen("C:\\Users\\Dishant\\Desktop\\Collection-DEV c++\\input.txt", "r", stdin);
        freopen("C:\\Users\\Dishant\\Desktop\\Collection-DEV c++\\output.txt", "w", stdout);
    }
    int t = 1;
    //cin>>t;
    while(t--) {
        solve();
    }
    return 0;
}
